Post-treatment system and engine system

Abstract

The present application provides an exhaust gas purification system and an engine system, which are less likely to have a reduced purification performance. An exhaust gas purification system (5) includes a connection path (71). The connection path (71) connects an exhaust port, from which exhaust gas is discharged in an engine main body (2), and an SCR device (51). The connection path (71) includes a first path (711) and a second path (712) each having a length in a direction intersecting each other, and a connection portion (713) connecting the first path (711) and the second path (712).

Description

Technical Field

[0001] This disclosure relates to after-treatment systems and engine systems. Background Technology

[0002] As related technology, an aftertreatment system (exhaust gas purification device) is known to have an SCR device (NOx purification catalyst) in the exhaust pipe through which exhaust gas (exhaust gas) flows from the engine body (internal combustion engine) (see, for example, Patent Document 1). The aftertreatment system of the related technology includes: a first SCR device disposed upstream in the direction of exhaust gas flow from the internal combustion engine; and a second SCR device disposed downstream of the first SCR device in the direction of exhaust gas flow.

[0003] Here, the aftertreatment system involved in the related technology includes an exhaust gas purification device (DOC and DPF), which is located between the first SCR device and the second SCR device to capture particulate matter in the exhaust gas. A reducing agent supply device (urea water injection device) for supplying reducing agent (urea water) is respectively arranged upstream of the first SCR device and upstream of the second SCR device.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2021-131068

[0005] However, in the aforementioned related technologies, for example, if the connection path from the exhaust port of the engine block to the first SCR device is shortened, the reducing agent may not be fully decomposed, resulting in a reduction in the exhaust gas purification performance of the first SCR device. On the other hand, if the connection path is lengthened, for example, the first SCR device may not be able to heat up quickly after the engine block is started, and the first SCR device may need time to reach its activation temperature, resulting in a reduction in the exhaust gas purification performance immediately after the engine block is started. Summary of the Invention

[0006] The purpose of this disclosure is to provide an aftertreatment system and an engine system with exhaust gas purification performance that is not easily reduced.

[0007] One aspect of the aftertreatment system disclosed herein includes a connection path. This connection path connects the exhaust port for discharging exhaust gases in the engine body to the aforementioned SCR device. The connection path includes a first path and a second path, each having length in intersecting directions, and a connecting portion linking the first path and the second path.

[0008] One embodiment of this disclosure relates to an engine system comprising the aforementioned after-treatment system and the aforementioned engine body.

[0009] According to this disclosure, an aftertreatment system and an engine system are provided that do not easily reduce the purification performance of exhaust gases. Attached Figure Description

[0010] Figure 1 This is a system diagram showing the general structure of the engine system involved in Embodiment 1.

[0011] Figure 2 This is a schematic perspective view of the engine body of the engine system involved in Embodiment 1.

[0012] Figure 3 This is a schematic perspective view of the engine body of the engine system involved in Embodiment 1.

[0013] Figure 4 This is a schematic left-side view of the engine body of the engine system involved in Embodiment 1.

[0014] Figure 5 This is a schematic diagram showing the structure of the exhaust gas recirculation system in the engine system involved in Embodiment 1.

[0015] Figure 6 This is a schematic diagram showing the structure of the after-treatment system of the engine system involved in Embodiment 1.

[0016] Figure 7 This is a schematic diagram showing the operation of the exhaust gas recirculation system of the engine system according to Embodiment 1 in the cooling mode.

[0017] Figure 8 This is a schematic diagram showing the operation of the exhaust gas recirculation system of the engine system according to Embodiment 1 in bypass mode.

[0018] Figure 9 This is a table showing an example of the operation of the exhaust gas recirculation system of the engine system involved in Embodiment 1.

[0019] Figure 10 This is a flowchart illustrating an example of the operation of the exhaust gas recirculation system of the engine system involved in Embodiment 1.

[0020] Figure 11 This is a flowchart illustrating an example of the operation of the exhaust gas recirculation system of the engine system involved in Embodiment 1.

[0021] Figure 12 This is a schematic cross-sectional view of the engine body of the engine system involved in Embodiment 1.

[0022] Figure 13 It is a schematic cross-sectional view of the connection path periphery of the engine body of the engine system involved in Embodiment 1, after being enlarged.

[0023] Figure 14This is a schematic perspective view of a portion of the engine body of the engine system involved in Embodiment 1 after it has been cut off.

[0024] Figure 15 This is a schematic cross-sectional view of the connection path periphery of the engine body of the engine system involved in the modified example of embodiment 1.

[0025] Figure 16 This is a schematic diagram showing the structure of the after-treatment system of the engine system involved in Embodiment 1.

[0026] Figure 17 This is a table showing examples of the operation of the after-processing system of the engine system involved in Implementation 1.

[0027] Figure 18 This is a flowchart illustrating an example of the operation of the after-processing system of the engine system involved in Embodiment 1.

[0028] Figure 19 This is a schematic left-side view of the engine system involved in Embodiment 2.

[0029] Figure 20 This is a schematic top view of the engine system involved in Embodiment 2.

[0030] Explanation of reference numerals in the attached figures

[0031] 1, 1A… Engine system; 2… Engine body; 5… Aftertreatment system; 11… Control unit; 51… (First) SCR device; 53… Exhaust gas purification device; 56… (First) Reductant supply device; 71… Connection path; 202… Exhaust port; 711… First path; 712… Second path (straight section); 713… Connecting part. Detailed Implementation

[0032] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. These embodiments are merely examples embodying the present disclosure and are not intended to limit the technical scope of the present disclosure. The accompanying drawings referenced in this disclosure are schematic diagrams, and the size and thickness ratios of the constituent elements in the drawings may not reflect actual dimensional ratios.

[0033] (Implementation Method 1)

[0034] [1] Overall structure

[0035] First, refer to Figures 1-6 The overall structure of the engine system 1 involved in this embodiment will be described. Figure 1 The diagram schematically shows the structure of each part of the engine system 1, and the electrical connections are indicated by dotted arrows (in the direction of the flow of electrical signals).

[0036] like Figure 1 As shown, the engine system 1 according to this embodiment includes an engine body 2, which is the main structure of the engine system 1. Here, "engine" refers to a heat engine that generates mechanical energy (power) by burning fuel. An internal combustion engine is a prime mover that converts thermal energy into mechanical energy by burning fuel inside the heat engine and using the combustion gases as moving gases. In other words, the engine body 2 generates power (mechanical energy) using the supplied fuel.

[0037] The engine body 2 involved in this embodiment is a reciprocating engine that converts the reciprocating motion of a piston into rotational motion and outputs rotational force as power. In particular, in this embodiment, a diesel engine that uses light oil as fuel, that is, a diesel reciprocating engine, will be used as an example of the engine body 2.

[0038] Engine systems 1 are used, for example, in various operational vehicles, ships, or aircraft. As an example, operational vehicles include agricultural machinery (farm machinery) such as tractors, rice transplanters, and combine harvesters, and construction machinery (construction machinery) such as backhoe excavators (including hydraulic excavators and mini excavators), wheel loaders, and transport vehicles. Ships include merchant ships such as yachts, cargo ships, and passenger / cargo ships; operational vessels such as tugboats and rescue ships; special vessels such as meteorological observation ships and training ships; fishing vessels; and warships. Aircraft include unmanned aerial vehicles (UAVs) or multi-rotor aircraft.

[0039] The engine system 1 is mounted on the fuselage of the mobile body. That is, the mobile body according to this embodiment includes the engine system 1 and the fuselage. The engine system 1 is used as a drive source for generating propulsion force to propel the fuselage and / or driving force to drive work machines, etc. In this embodiment, the engine system 1 can also be used as a drive source to drive a generator that generates electrical energy (electricity) used in the fuselage. In other words, the engine system 1 is used to generate propulsion force and / or driving force for the fuselage of the mobile body or as a drive source for driving a generator. The electrical energy generated in the generator can also be stored in an energy storage device.

[0040] In this embodiment, as an example, engine system 1 is used in a tractor used for field operations. A tractor is a type of work vehicle that moves across a field using power generated in engine system 1. The tractor uses the power generated in engine system 1 to drive the rear wheels, which serve as drive wheels, thereby generating a propulsive force to move the tractor forward or backward.

[0041] The engine body 2 is, for example, installed inside the engine hood of the tractor's body. Here, as... Figures 2-4 As shown, the engine body 2 is arranged with the cylinder block 21 and cylinder head 22 stacked in the vertical direction D2. Specifically, the engine body 2 is arranged with the cylinder head 22 above the cylinder block 21 and the crankshaft 23's rotation axis Ax1 oriented in a generally horizontal direction.

[0042] Furthermore, in this embodiment, the mobile body (tractor) equipped with the engine system 1 is designed to operate according to the operation of a person (operator), including remote operation, and is particularly a manned type that can be ridden by a person acting as the operator. Therefore, the mobile body has an operating device in its fuselage that receives the operator's operations, and the control unit 11 of the engine system 1 (see reference 1) controls the operation of the operating device. Figure 1 The engine body 2 is driven. Thus, the moving body drives the engine body 2 and rotates the drive wheels according to the operator's operation, thereby enabling the fuselage to move forward or backward.

[0043] In addition, for ease of explanation in this embodiment, as follows: Figure 2 As shown, the direction along the rotation axis Ax1 of crankshaft 23 is defined as the output shaft direction D1. Furthermore, as... Figure 2 As shown, the direction orthogonal to the output shaft direction D1 and along the vertical direction in the usable state of the engine body 2 is defined as the vertical direction D2, and the direction orthogonal to both the output shaft direction D1 and the vertical direction D2 is defined as the width direction D3. Here, one side of the output shaft direction D1 is defined as "front", and the other side is defined as "rear", with the side of the crankshaft 23 where the flywheel 24 is located designated as the rear. Similarly, one side of the width direction D3 is defined as "left", and the other side is defined as "right". Furthermore, in the vertical direction D2, the side where the cylinder head 22 is located when viewed from the cylinder block 21 is defined as "upper", and the opposite side is defined as "lower".

[0044] In other words, all directions used in this embodiment are defined with reference to the rotation axis Ax1 of the crankshaft 23. However, none of the above directions are intended to limit the direction of use of the engine body 2 (the direction during use).

[0045] In the engine body 2, the rotational force of the crankshaft 23, which serves as the engine output shaft, is output. The crankshaft 23 is connected to drive wheels via a transmission or the like. When the engine body 2 is driven and the crankshaft 23 rotates around the rotation axis Ax1, the drive wheels rotate, and the tractor can move.

[0046] As described above, the engine system 1 involved in this embodiment is a diesel engine. Therefore, the engine body 2 is configured to be able to supply fuel (here, light oil) from outside the engine body 2. That is, as... Figure 1 As shown, the engine system 1 includes a fuel supply device 3 for supplying fuel.

[0047] In addition, such as Figure 1 As shown, the engine system 1 according to this embodiment further includes: an exhaust gas recirculation system 4, an aftertreatment system 5, and a control unit 11. The exhaust gas recirculation system 4 is a system that recirculates at least a portion of the exhaust gas discharged from the engine body 2 as EGR (Exhaust Gas Recirculation) gas from the exhaust port 202 of the engine body 2 back to the intake port 201. The aftertreatment system 5 is a system for purifying the exhaust gas discharged from the engine body 2. That is, the engine system 1 includes, in addition to the engine body 2, a fuel supply device 3, an exhaust gas recirculation system 4, and an aftertreatment system 5.

[0048] like Figures 2-4 As shown, the engine body 2 is constructed by assembling the cylinder head 22 onto the cylinder block 21. The cylinder block 21 has cylinders 211 (see reference). Figure 5 The cylinder head 22 has intake and exhaust ports. Figure 2 and Figure 3 As shown, the crankshaft 23 is rotatably supported on the cylinder block 21 with the rotating shaft Ax1 facing the output shaft direction D1.

[0049] In the cylinder block 21, a plurality of cylinders 211 (four in this embodiment, for example) are arranged in a row (in a straight line) along the rotation axis Ax1 of the crankshaft 23. That is, in this embodiment, the engine body 2 is an inline multi-cylinder engine (inline 4-cylinder engine) in which the plurality of cylinders 211 are arranged in a straight line. The output shaft direction D1 along the rotation axis Ax1 of the crankshaft 23 is consistent with the arrangement direction of the plurality of cylinders 211. The piston is housed in each cylinder 211 in a manner that allows it to slide in the vertical direction D2, that is, to reciprocate. The piston is connected to the crankshaft 23 via a connecting rod.

[0050] Multiple cylinder heads 22 are fixed to the cylinder block 21 from above, covering the cylinders 211. The space inside each cylinder 211, surrounded by the upper surface of the piston and the lower surface of the cylinder head 22, functions as a combustion chamber. That is, the piston reciprocates in the vertical direction D2, causing the combustion chamber to alternately expand and contract repeatedly.

[0051] The cylinder head 22 is equipped with, for example, a valve mechanism including pushrods and rocker arms for actuating the intake and exhaust valves. The intake valve opens and closes an opening in the intake port of the cylinder head 22 that connects to the combustion chamber. The exhaust valve opens and closes an opening in the exhaust port of the cylinder head 22 that connects to the combustion chamber. Thus, when the intake valve is open, air from the intake port (intake air) can be drawn into the combustion chamber. When the exhaust valve is open, exhaust gas from the combustion chamber can be discharged to the exhaust port.

[0052] In addition, the engine body 2 is provided with an intake manifold 25 for distributing air (intake air) from outside the engine body 2 to the interior of the engine body 2 (the combustion chamber of each cylinder 211). Furthermore, the engine body 2 is provided with an exhaust manifold 26 for collecting the exhaust gas generated by combustion in the combustion chamber of each cylinder 211 and discharging it to the outside of the engine body 2.

[0053] like Figure 3 As shown, the intake manifold 25 is located on the right side of the cylinder head 22. The intake manifold 25 extends along the output shaft direction D1 and connects to multiple intake ports formed in the cylinder head 22. Thus, air is distributed from the intake manifold 25 to the multiple intake ports. In other words, the intake manifold 25 communicates with the combustion chamber of each cylinder 211 through the intake ports.

[0054] like Figure 2 As shown, the exhaust manifold 26 is located to the left of the cylinder head 22. The exhaust manifold 26 extends along the output shaft direction D1 and connects to multiple exhaust ports formed in the cylinder head 22. Thus, exhaust gases from the multiple exhaust ports are collected in the exhaust manifold 26. In other words, the exhaust manifold 26 communicates with the combustion chamber of each cylinder 211 through the exhaust ports.

[0055] Here, the main components constituting the engine body 2, such as the cylinder block 21, cylinder head 22, intake manifold 25, and exhaust manifold 26, are made of metal materials such as aluminum alloy and cast iron. These main components have the desired durability (including rigidity and wear resistance) and relatively excellent thermal conductivity.

[0056] According to the above structure, when the engine body 2 is driven, fuel is injected into the combustion chamber from the fuel supply device 3 at an appropriate moment when the air supplied from the intake manifold 25 to each cylinder 211 is compressed due to piston sliding. The injection of fuel into the combustion chamber causes the piston to reciprocate within the cylinder 211 by the thrust generated by the detonation in the combustion chamber. This reciprocating motion of the piston is converted into the rotational motion of the crankshaft 23 via the connecting rod. Thus, the engine body 2 outputs the rotational force of the crankshaft 23 as power (mechanical energy).

[0057] Furthermore, when the engine body 2 is driven, the exhaust gas generated by combustion (detonation) in the combustion chamber is squeezed out of the cylinder 211 by the movement of the piston, and is collected in the exhaust manifold 26 through the exhaust port, and then discharged to the outside of the engine body 2.

[0058] The fuel supply device 3 has an injection section connected to the fuel tank via a fuel supply passage. The fuel supply device 3 injects fuel supplied via the fuel supply passage into the engine body 2 from the nozzle-shaped (cylindrical) injection section. Here, the injection section is positioned facing the combustion chamber. Thus, the injection section directly injects fuel into the combustion chamber.

[0059] The exhaust gas recirculation system 4 re-intakes (recirculates) a portion of the exhaust gas generated in the engine body 2 back into the engine body 2. The exhaust gas recirculation system 4 is connected to the air intake port 201 in the engine body 2, which serves as an air intake. In this embodiment, as... Figure 5 As shown, the connection of the intake path 27 in the intake manifold 25 is the intake port 201, and the connection of the exhaust path 28 in the exhaust manifold 26 is the exhaust port 202. That is, an exhaust gas recirculation system 4 is inserted between the intake path 27 used to obtain air to the intake manifold 25 and the exhaust path 28 connected to the exhaust manifold 26.

[0060] The exhaust gas recirculation system 4 uses at least a portion of the air (exhaust gas) discharged from the engine body 2 as EGR gas, and recirculates it from the exhaust port 202 (of the exhaust manifold 26) of the engine body 2 to the intake port 201 (of the intake manifold 25). In other words, the EGR gas is a portion of the air (exhaust gas) discharged from the exhaust manifold 26 of the engine body 2, and it is air that is re-intaken (recirculated) into the intake manifold 25 of the engine body 2. The exhaust gas recirculation system 4 recirculates the EGR gas, thereby reducing the combustion temperature and helping to suppress the production of nitrogen oxides (NOx) and improve fuel efficiency.

[0061] The aftertreatment system 5 purifies the exhaust gas discharged from the engine body 2, thereby enabling the engine system 1 to meet the desired emission limits. The aftertreatment system 5 is inserted into the exhaust path 28, which is connected to the exhaust port 202 of the engine body 2 (exhaust manifold 26). Thus, the air (exhaust gas) discharged to the outside of the engine system 1 through the exhaust path 28 passes through the aftertreatment system 5 and is purified in the aftertreatment system 5.

[0062] In this embodiment, such as Figure 6 As shown, the aftertreatment system 5 includes: a first SCR (Selective Catalytic Reduction) device 51, a second SCR device 52, and an exhaust gas purification device 53. The first SCR device 51 is also simply referred to as "SCR device 51".

[0063] Each of the first SCR device 51 and the second SCR device 52 converts nitrogen oxides (NOx) in the exhaust gas passing through exhaust path 28 into nitrogen molecules (N2) and water (H2O) through a catalyst, thereby reducing nitrogen oxides in the exhaust gas.

[0064] Each of the first SCR device 51 and the second SCR device 52 is a catalyst that reduces nitrogen oxides in the exhaust gas to nitrogen gas by using ammonia gas generated from urea (an example of a reducing agent) injected into the exhaust path 28. Here, urea, as an example of a reducing agent, is hydrolyzed by the exhaust heat (heat of the exhaust gas) of the engine body 2 and is thus blown into the exhaust gas to become ammonia gas. Through this mechanism, each of the first SCR device 51 and the second SCR device 52 reduces nitrogen oxides in the exhaust gas, thereby purifying the exhaust gas.

[0065] The exhaust gas purification device 53 captures particulate matter in the exhaust gas passing through the exhaust path 28. In this embodiment, such as Figure 6 As shown, the exhaust gas purification device 53 is located between the first SCR device 51 and the second SCR device 52 in the exhaust path 28. The exhaust gas purification device 53 is a diesel particulate filter (DPF) device that captures particulate matter (PM) such as soot contained in the exhaust gas.

[0066] That is, the exhaust gas purification device 53 has an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 531 and a particulate filter (SF: Soot Filter) 532. The exhaust gas purification device 53 decomposes particulate matter in the exhaust gas through the oxidation catalyst 531 and captures it using the particulate filter 532, thereby preventing harmful substances from being released into the atmosphere. If the particulate matter captured by the particulate filter 532 remains unchanged, it will cause blockage of the particulate filter 532. Therefore, the particulate filter 532 needs to be regenerated in the exhaust gas purification device 53.

[0067] The control unit 11 is primarily structured as a computer system having one or more processors such as a CPU (Central Processing Unit) and one or more memories such as ROM (Read Only Memory) and RAM (Random Access Memory), and performs various processes (information processing). The control unit 11 stores programs (engine control programs) in one or more memories for causing one or more processors to execute engine control methods.

[0068] The control unit 11 outputs control signals (electrical signals) to the engine body 2, fuel supply device 3, exhaust gas recirculation system 4, and aftertreatment system 5, thereby controlling these components. Thus, the control unit 11 can control the engine body 2 to adjust its output (primarily engine speed) to any value. Furthermore, the control unit 11 can also control the intake throttle valve 271 (see reference...). Figure 5 The intake throttle valve 271 is located in the intake path 27 downstream of the compressor 61 in the intake air flow.

[0069] Furthermore, the engine system 1 involved in this embodiment includes a turbocharger 6 in addition to the engine body 2 (see reference). Figure 1 The engine is equipped with a supercharger. However, the supercharger 6 is not a necessary component of the engine system 1 and can be omitted appropriately.

[0070] like Figure 5 As shown, the turbocharger 6 includes a compressor 61 and a turbine 62. The compressor 61 is configured on the intake path 27 for drawing air to the intake manifold 25. The turbine 62 is configured on the exhaust path 28 connected to the exhaust manifold 26.

[0071] Turbine 62 is connected to compressor 61. When turbine 62 rotates due to the flow of air (exhaust gas) discharged through exhaust passage 28, compressor 61 rotates. As compressor 61 rotates, air (intake air) obtained from intake passage 27 is compressed and delivered to intake manifold 25 through internal cooler. Internal cooler cools the air (intake air) compressed by turbocharger 6. Figure 1 The thick arrows in the text indicate the flow of air (airflow), including both intake and exhaust air.

[0072] However, in addition to the above-described structure (engine body 2, fuel supply device 3, exhaust gas recirculation system 4, aftertreatment system 5, control unit 11, and turbocharger 6), the engine system 1 of this embodiment also includes an air filter 272 (see reference). Figure 5 ), various sensors 12 (refer to) Figure 1 )wait.

[0073] The air filter 272 is positioned upstream of the compressor 61 in the intake path 27, closer to the intake air flow. The sensor 12 includes a speed sensor for detecting the rotational speed of the engine block 2, a temperature sensor for measuring the temperature of exhaust gases, and a pressure sensor for measuring the pressure of exhaust gases, etc. The sensor 12 outputs an electrical signal corresponding to the measured value (rotational speed, temperature, or pressure, etc.) to the control unit 11.

[0074] [2] Details of the exhaust gas recirculation system

[0075] Next, refer to Figure 5 as well as Figures 7-11 Details of the exhaust gas recirculation system 4 involved in this embodiment will be described.

[0076] like Figure 5 As shown, the exhaust gas recirculation system 4 includes: an EGR path 41, an EGR valve 42, a cooling unit 43, a bypass path 44, and a switching valve 45. Here, the control unit 11 is capable of controlling the exhaust gas recirculation system 4, specifically the EGR valve 42 and the switching valve 45, and is therefore considered a component of the exhaust gas recirculation system 4.

[0077] EGR path 41 is a piping that connects the exhaust port 202 of the engine body 2 to the intake port 201 and allows gas (EGR gas) to pass through. Specifically, EGR path 41 branches off from exhaust path 28, which is connected to the exhaust port 202 of exhaust manifold 26, and connects to intake path 27, thereby connecting exhaust port 202 to intake port 201. Through such EGR path 41, EGR gas, which consists of at least a portion of the exhaust gas, can flow back from exhaust port 202 of engine body 2 to intake port 201.

[0078] EGR valve 42 is inserted into EGR path 41. EGR valve 42 can regulate the flow rate of EGR gas returning from exhaust port 202 to intake port 201 of engine body 2 through EGR path 41. That is, the larger the opening of EGR valve 42, the larger the flow rate of EGR gas; the smaller the opening of EGR valve 42, the smaller the flow rate of EGR gas. When EGR valve 42 is fully closed, the EGR gas flowing in EGR path 41 is cut off, and the return flow of EGR gas from exhaust port 202 to intake port 201 stops. In this embodiment, EGR valve 42 is a solenoid valve whose opening can be adjusted by a control signal from control unit 11.

[0079] The cooling unit 43 is an EGR cooler that cools the EGR gas. The cooling unit 43 is inserted into the EGR path 41 in series with the EGR valve 42. The cooling unit 43 has a cooling path 431 included in the EGR path 41, and cools the EGR gas passing through the cooling path 431. The cooling unit 43 uses a refrigerant such as cooling water, and cools the EGR gas passing through the cooling path 431 by heat exchange with it. In this embodiment, as an example, the cooling unit 43 uses cooling water from the engine body 2 as the refrigerant.

[0080] The bypass path 44 is a piping that connects the inlet and outlet of the cooling path 431 and allows gas (EGR gas) to pass through. The bypass path 44 is inserted into the EGR path 41 in series with the EGR valve 42. Here, the bypass path 44 is connected in parallel to the EGR path 41 that connects the exhaust port 202 and the intake port 201. Therefore, when the EGR gas passes through the bypass path 44, the cooling section 43 (cooling path 431) is bypassed.

[0081] A switching valve 45 is inserted into the EGR path 41. The switching valve 45 is located on the EGR path 41, in the direction of EGR gas flow, upstream of the cooling section 43 (cooling path 431) and the bypass path 44 (that is, on the exhaust port 202 side). The switching valve 45 is located at the branch point between the cooling section 43 (cooling path 431) and the bypass path 44, switching the path through which EGR gas passes between the cooling section 43 (cooling path 431) and the bypass path 44. In other words, according to the switching valve 45, the EGR gas passing through the EGR path 41 passes through either the cooling section 43 (cooling path 431) or the bypass path 44. In this embodiment, the switching valve 45 is a solenoid valve that switches the connection destination of the exhaust port 202 between the cooling section 43 (cooling path 431) and the bypass path 44, and can be switched by a control signal from the control unit 11.

[0082] Here, the EGR valve 42, cooling unit 43, bypass path 44, and switching valve 45 are connected in the direction of EGR gas flow, starting from the upstream side (that is, the exhaust port 202 side), in the order of switching valve 45, cooling unit 43, bypass path 44, and EGR valve 42.

[0083] According to the above structure, if the EGR valve 42 is in the open state, the exhaust gas recirculation system 4 can use at least a portion of the exhaust gas discharged from the engine body 2 as EGR gas to flow back from the exhaust port 202 of the engine body 2 to the intake port 201.

[0084] Furthermore, the exhaust gas recirculation system 4 can be switched via valve 45. Figure 7 The cooling modes shown and Figure 8 The bypass mode is switched as shown. That is, the exhaust gas recirculation system 4, which recirculates EGR gas, is prepared with a cooling mode and a bypass mode as its operating modes.

[0085] like Figure 7As shown, the cooling mode is the operating mode in which the cooling section 43 (cooling path 431) is selected as the path for EGR gas through the switching valve 45. With the EGR valve 42 in the open state, if the exhaust gas recirculation system 4 is in cooling mode, the EGR gas passes through the cooling section 43 (cooling path 431) and flows back from the exhaust port 202 of the engine body 2 to the intake port 201. Therefore, the EGR gas passing through the EGR path 41 is cooled in the cooling section 43, and its temperature decreases as it passes through the EGR path 41.

[0086] On the other hand, such as Figure 8 As shown, the bypass mode is the operating mode in which the bypass path 44 is selected as the path for EGR gas through the switching valve 45. With the EGR valve 42 in the open state, if the exhaust gas recirculation system 4 is in bypass mode, the EGR gas flows back from the exhaust port 202 to the intake port 201 of the engine body 2 through the bypass path 44. Therefore, the EGR gas passing through the EGR path 41 does not pass through the cooling section 43 (cooling path 431), and the temperature of the EGR gas does not decrease when passing through the EGR path 41.

[0087] However, in this embodiment, when the determination conditions are met, the control unit 11 performs EGR gas recirculation in the bypass mode, which directs the EGR gas to the bypass path 44 to bypass the cooling path 431. In other words, the control unit 11 controls the switching valve 45 based on whether the determination conditions are met; if the conditions are met, the bypass mode is selected; otherwise, the cooling mode is selected. Specifically, based on determining whether predetermined determination conditions are met, the control unit 11 performs EGR gas recirculation in the bypass mode if the conditions are met.

[0088] In summary, the exhaust gas recirculation system 4 according to this embodiment can switch between two operating modes: cooling mode and bypass mode, when the EGR valve 42 is opened and EGR gas recirculation is in the "EGR ON" state. Therefore, the exhaust gas recirculation system 4 can switch between three states: "EGR OFF" state (when the EGR valve 42 is closed and EGR gas recirculation is stopped), "EGR ON" state (cooling mode), and "EGR ON" state (bypass mode).

[0089] As explained above, the exhaust gas recirculation system 4 according to this embodiment is a system that recirculates at least a portion of the exhaust gas discharged from the engine body 2 as EGR gas from the exhaust port 202 to the intake port 201 of the engine body 2. The exhaust gas recirculation system 4 includes: an EGR path 41, a cooling unit 43, a bypass path 44, and a control unit 11. The EGR path 41 connects the exhaust port 202 and the intake port 201, allowing EGR gas to pass through. The cooling unit 43 has a cooling path 431 included in the EGR path 41, and cools the EGR gas passing through the cooling path 431. The bypass path 44 connects the inlet (upstream side in the flow direction of the EGR gas) and the outlet (downstream side in the flow direction of the EGR gas) of the cooling path 431. When a determination condition is met, the control unit 11 performs EGR gas recirculation in a bypass mode, causing the EGR gas to flow to the bypass path 44 to bypass the cooling path 431.

[0090] According to this structure, for example, under conditions such as extremely low exhaust gas temperature, EGR gas recirculation can be performed in a bypass mode where EGR gas flows to the bypass path 44 to bypass the cooling path 431 under specific conditions. Therefore, even under these specific conditions, EGR gas recirculation can be performed, and over-cooling of the EGR gas by the cooling section 43 can be prevented, as well as the generation of incomplete combustion products (engine deposits) in the EGR valve 42 and the like can be suppressed. As a result, in this embodiment, an exhaust gas recirculation system 4 that is less prone to generating engine deposits, an engine system 1 equipped with the exhaust gas recirculation system 4, and a control method and control program for the exhaust gas recirculation system 4 can be provided.

[0091] More specifically, for example, when the engine block 2 operates continuously under light load (low load), the exhaust gas temperature cannot rise sufficiently, resulting in a "low exhaust gas temperature" state. In this "low exhaust gas temperature" state, if the exhaust gas recirculation system 4 recirculates EGR gas in a cooling mode that directs EGR gas to the cooling path 431 for cooling, there is a possibility of over-cooling of the EGR gas and accumulation of engine deposits on the EGR valve 42. If engine deposits accumulate, it may lead to adverse conditions such as reduced EGR gas flow through the EGR path 41, resulting in worsened emissions, or malfunction of the EGR valve 42 when the amount of engine deposits is too large. Therefore, to avoid these adverse conditions, it is advisable to fundamentally close the EGR valve 42 and stop the recirculation of EGR gas (EGR OFF) in the "low exhaust gas temperature" state. Figure 9 (Comparative example).

[0092] In contrast, in the exhaust gas recirculation system 4 of this embodiment, EGR gas is recirculated in bypass mode when the determination conditions are met. Therefore, even in conditions such as "low exhaust gas temperature," the EGR valve 42 can be opened to allow EGR gas recirculation (EGR ON). In other words, even when recirculating EGR gas in conditions such as "low exhaust gas temperature," the exhaust gas recirculation system 4 of this embodiment can suppress excessive cooling of the EGR gas and avoid the aforementioned adverse conditions caused by engine deposits.

[0093] Furthermore, the exhaust gas recirculation system 4 according to this embodiment includes an EGR valve 42 that regulates the flow rate of EGR gas passing through the EGR path 41. Thus, the flow rate of the recirculating EGR gas can be regulated by adjusting the opening degree of the EGR valve 42. Moreover, when certain conditions are met, EGR gas recirculation occurs in bypass mode, thereby suppressing the accumulation of engine deposits in the EGR valve 42.

[0094] Furthermore, the exhaust gas recirculation system 4 according to this embodiment includes a switching valve 45 disposed in the EGR path 41. The switching valve 45 switches the path through which the EGR gas passes between the cooling section 43 (cooling path 431) and the bypass path 44. Thus, by controlling the switching valve 45, it is possible to switch between a cooling mode that cools the EGR gas and a bypass mode that allows the EGR gas to flow to the bypass path 44, thereby bypassing the cooling section 43 (cooling path 431).

[0095] In this embodiment, the determination criteria include conditions related to the temperature of the exhaust gas. That is, the control unit 11 determines whether the determination criteria are met based on the temperature of the exhaust gas measured by the temperature sensor included in the sensor 12. For example, the exhaust gas temperature is measured near the exhaust port 202 of the exhaust manifold 26. As an example, the determination criteria include the exhaust gas temperature being below a predetermined exhaust gas reference temperature, and / or the rate of change of the exhaust gas temperature per unit time being below a predetermined value. Therefore, even when the exhaust gas recirculation system 4 performs EGR gas recirculation under conditions such as "low exhaust gas temperature," it can suppress excessive cooling of the EGR gas and avoid the aforementioned adverse conditions caused by engine deposits.

[0096] Furthermore, the determination condition includes the stability of the EGR gas flow. That is, based on the condition of stable EGR gas flow, the control unit 11 performs EGR gas recirculation in bypass mode, which directs the EGR gas to the bypass path 44 to bypass the cooling path 431. As a result, EGR gas recirculation in bypass mode under unstable EGR gas flow conditions can be avoided, and overcooling of the EGR gas can be easily suppressed.

[0097] Here, if the temperature of the EGR gas remains below the EGR gas reference temperature for a certain period of time, the control unit 11 determines that the flow of the EGR gas is stable. In other words, the control unit 11 determines whether the flow of the EGR gas, which serves as a determination condition, is stable based on whether the temperature of the EGR gas has remained below the EGR gas reference temperature for a certain period of time. Specifically, the control unit 11 determines whether the determination condition is met based on the temperature of the EGR gas measured by the temperature sensor included in the sensor 12. For example, the temperature of the EGR gas is measured at the position between the cooling unit 43 and the EGR valve 42 in the EGR path 41. Therefore, even without directly monitoring the flow of the EGR gas, it is possible to determine whether the flow of the EGR gas is stable.

[0098] Furthermore, in this embodiment, the determination condition includes the temperature of the refrigerant used for cooling the engine body 2. In this embodiment, the refrigerant (cooling water) used for cooling the engine body 2 is also used in the cooling unit 43 for cooling the EGR gas. The control unit 11 determines whether the determination condition is met based on the temperature of the refrigerant measured by the temperature sensor included in the sensor 12. For example, the temperature of the refrigerant is measured in the cooling unit 43. As an example, the determination condition includes the refrigerant temperature being below a predetermined refrigerant reference temperature and / or the rate of change of the refrigerant temperature per unit time being below a predetermined value. Thus, even when the exhaust gas recirculation system 4 performs EGR gas recirculation in a "low water temperature" state, such as immediately after the engine body 2 starts, where the refrigerant temperature has not risen and the refrigerant temperature is relatively low, it can suppress over-cooling of the EGR gas.

[0099] Furthermore, when the exhaust gas temperature is below the first reference temperature and the temperature of the refrigerant (cooling water) cooling the engine body 2 is below the refrigerant reference temperature, the control unit 11 stops the EGR gas recirculation. In other words, when the exhaust gas temperature is below the first reference temperature and the temperature of the refrigerant cooling the engine body 2 is below the refrigerant reference temperature, the control unit 11 determines that the stopping condition is met, closes the EGR valve 42, and stops the EGR gas recirculation (EGR OFF). Thus, when the exhaust gas temperature is extremely low and the refrigerant temperature is also relatively low, the EGR gas recirculation can be stopped, thereby preventing the accumulation of engine deposits.

[0100] Here, the determination criteria include an exhaust gas temperature higher than a first reference temperature and lower than a second reference temperature, and a refrigerant temperature lower than a refrigerant reference temperature. The second reference temperature is a temperature higher than the first reference temperature. In other words, even if the refrigerant temperature is lower than the refrigerant reference temperature, if the exhaust gas temperature is not lower than the first reference temperature (but higher than the first reference temperature) and is lower than the second reference temperature, the control unit 11 does not stop the EGR gas recirculation, but performs EGR gas recirculation in bypass mode. Therefore, EGR gas recirculation can be performed as much as possible while suppressing overcooling of the EGR gas.

[0101] Furthermore, in this embodiment, the control unit 11 can switch the EGR gas recirculation / stop during the regeneration of the exhaust gas purification device 53 that captures particulate matter in the exhaust gas. That is, when the particulate filter 532 needs to be regenerated in the exhaust gas purification device 53, the control unit 11 can control the EGR valve 42 during the regeneration to switch the EGR gas recirculation / stop.

[0102] During the regeneration of the exhaust gas purification device 53, the temperature of the exhaust gas is sometimes raised by injecting unburned fuel into the oxidation catalyst 531. In this case, if the EGR gas contains an excessive amount of unburned fuel components (THC: Total Hydrocarbon), engine deposits may be generated due to these unburned fuel components. Therefore, for example, in Figure 9 In the comparative example shown, the control unit 11 unconditionally closes the EGR valve 42 and stops the backflow of EGR gas (EGR OFF) when the exhaust gas purification device 53 is regenerated (DPF regeneration operation).

[0103] In contrast, in this embodiment, even during the regeneration of the exhaust gas purification device 53, the EGR gas recirculation is not unconditionally stopped; instead, the recirculation / stopping of EGR gas is switched based on switching conditions. For example, even during the regeneration of the exhaust gas purification device 53, EGR gas recirculation is permitted when engine deposits are unlikely to form. Therefore, even during the regeneration of the exhaust gas purification device 53, EGR gas recirculation can be performed as much as possible.

[0104] Furthermore, when the control unit 11 switches the EGR gas recirculation / stop during the regeneration of the exhaust gas purification device 53 that captures particulate matter in the exhaust gas, switching between cooling mode and bypass mode is not necessary. In other words, bypass path 44 can also be omitted.

[0105] In this configuration, the exhaust gas recirculation system 4 is a system that recirculates at least a portion of the exhaust gas discharged from the engine block 2 as EGR gas from the exhaust port 202 to the intake port 201 of the engine block 2. The exhaust gas recirculation system 4 may include an EGR path 41 and a control unit 11. The EGR path 41 connects the exhaust port 202 to the intake port 201, allowing EGR gas to pass through. The control unit 11 can switch the recirculation / stopping of EGR gas during the regeneration of the exhaust gas purification device 53 that captures particulate matter in the exhaust gas.

[0106] Here, the control unit 11 recirculates the EGR gas when the regeneration of the exhaust gas purification device 53 is without post-injection, and stops the EGR gas recirculation when there is post-injection. In other words, the switching conditions include the presence or absence of post-injection. As the regeneration mode of the exhaust gas purification device 53, there are active (forced) regeneration mode with post-injection and passive regeneration mode without post-injection. In active regeneration mode, the temperature of the exhaust gas is forcibly raised by post-injection, which delays the injection of fuel compared to the main combustion injection period, and the unburned fuel is delivered to the oxidation catalyst 531, causing the particulate matter accumulated in the particulate trap 532 to burn.

[0107] During the regeneration of the exhaust gas purification device 53, if the regeneration mode of the exhaust gas purification device 53 is an active regeneration mode with after-injection, the control unit 11 closes the EGR valve 42 to stop the backflow of EGR gas (EGR OFF). On the other hand, if the regeneration mode of the exhaust gas purification device 53 is a passive regeneration mode without after-injection, the control unit 11 opens the EGR valve 42 to allow the EGR gas to flow back (EGR ON). Therefore, when there is an after-injection where the EGR gas may contain excessive amounts of unburned fuel components (THC), the exhaust gas recirculation system 4 can stop the backflow of EGR gas, thereby suppressing the formation of engine deposits caused by unburned fuel components. Furthermore, during regeneration without after-injection, the exhaust gas recirculation system 4 can allow the EGR gas to flow back, thereby reducing emissions.

[0108] However, when the exhaust gas purification device 53 is regenerated, the control unit 11 performs restricted backflow while allowing EGR gas to flow through. That is, during the regeneration of the exhaust gas purification device 53, the EGR gas is not allowed to flow through as it does during normal operation of the engine body 2; instead, the backflow of the EGR gas is restricted. This, for example, can suppress the formation of engine deposits caused by unburned fuel components contained in the EGR gas.

[0109] In this embodiment, the restricted recirculation during the regeneration of the exhaust gas purification device 53 includes the recirculation of EGR gas in bypass mode. Therefore, during the regeneration of the exhaust gas purification device 53, the recirculation of EGR gas is not stopped, and it can be performed in bypass mode. Thus, the recirculation of EGR gas can be performed as much as possible while suppressing excessive cooling of the EGR gas.

[0110] Figure 9 The operation of the exhaust gas recirculation system 4 according to this embodiment is shown under various operating conditions. Figure 9 The operation of the exhaust gas recirculation system involved in the comparative example without bypass path 44 is also shown.

[0111] First, in the exhaust gas recirculation system involved in the comparative example, such as Figure 9 As shown, EGR gas recirculation (EGR ON) only occurs during normal operation (warm-up operation) of the engine main body 2. That is, under operating conditions other than normal operation (warm-up operation) of the engine main body 2, EGR gas recirculation is stopped (EGR OFF) in the exhaust gas recirculation system involved in the comparative example. Specifically, EGR gas recirculation stops in states such as "low coolant temperature" (cold state: low coolant temperature) during normal operation of the engine main body 2, where the refrigerant temperature has not risen and is relatively low, and "continuous light load operation (low exhaust gas temperature)" where the engine main body 2 operates continuously under light load. Furthermore, EGR gas recirculation stops even during the regeneration of the exhaust gas purification device 53 (DPF regeneration operation).

[0112] In contrast, in the exhaust gas recirculation system 4 of this embodiment, EGR gas is recirculated (EGR ON) even during normal operation (warm-up) of the engine body 2. Specifically, EGR gas is recirculated (EGR ON) even under operating conditions other than normal operation (warm-up) of the engine body 2.

[0113] However, during normal operation (warm-up) of the engine body 2, the exhaust gas recirculation system 4 operates in a cooling mode (bypass OFF) that prevents EGR gas from passing through the bypass path 44, cooling the EGR gas in the cooling section 43. On the other hand, under operating conditions other than normal operation (warm-up) of the engine body 2, the exhaust gas recirculation system 4 operates in a bypass mode (bypass ON) that allows EGR gas to pass through the bypass path 44, without cooling the EGR gas in the cooling section 43. Specifically, in the "low coolant temperature" state (cold state: low coolant temperature) and "continuous light load operation (low exhaust gas temperature)" states during normal operation of the engine body 2, the exhaust gas recirculation system 4 circulates EGR gas in a bypass mode without cooling the EGR gas. Even during the regeneration of the exhaust gas purification device 53 (DPF regeneration operation), the exhaust gas recirculation system 4 circulates EGR gas in bypass mode.

[0114] Furthermore, when the shutdown condition is met under operating conditions other than the normal operation (warm-up operation) of the engine main body 2, the exhaust gas recirculation system 4 closes the EGR valve 42 and stops the return of EGR gas (EGR OFF). That is, in the "low coolant temperature" state (cold state: low coolant temperature) and the "continuous light load operation (low exhaust gas temperature)" state of the engine main body 2, when the exhaust gas temperature is extremely low and the refrigerant temperature is also relatively low, the shutdown condition is met, therefore the exhaust gas recirculation system 4 stops the circulation of EGR gas. During the regeneration of the exhaust gas purification device 53 (DPF regeneration operation), if the regeneration mode of the exhaust gas purification device 53 is the active regeneration mode with after-injection, then assuming the shutdown condition is met, the exhaust gas recirculation system 4 stops the circulation of EGR gas.

[0115] However, the cooling section 43 (cooling path 431) and the bypass path 44 may also be formed in at least one of the exhaust manifold 26 and the cylinder head 22, and a switching valve 45 may be mounted in at least one of the intake manifold 25 and the cylinder head 22. That is, the EGR path 41 branches into the cooling path 431 and the bypass path 44 from the downstream end in the flow direction of the EGR gas to the downstream end, and the switching valve 45 is located downstream of the cooling path 431 and the bypass path 44. Here, inside the cylinder head 22, the cooling path 431 is located on the water jacket side through which the refrigerant (cooling water) passes, and the bypass path 44 is located on the outside. Furthermore, it is preferable to sandwich an air layer or other heat insulation layer between the water jacket and the bypass path 44.

[0116] In this structure, the switching valve 45 is mounted on the intake side where the ambient temperature is low, thus eliminating the need for cooling the switching valve 45. In bypass mode, the EGR gas is kept warm by passing through the bypass path 44 within the cylinder head 22 of the casting and is then returned at a higher temperature. On the other hand, in cooling mode, the EGR gas is also cooled by the water jacket of the cylinder head 22 as it passes through the cooling path 431, and is therefore returned at a lower temperature. Thus, the EGR gas can be returned to the intake port 201 at a lower temperature in cooling mode and at a higher temperature in bypass mode, allowing EGR gas to be introduced over a wider range of exhaust gas temperatures from low to high, thereby reducing exhaust gas composition.

[0117] Figure 10 This is a flowchart illustrating an example of the processing involved in the control method of the exhaust gas recirculation system 4 executed in the control unit 11, particularly the processing involved in the operation of the engine main body 2 during normal operation. Here, the first reference temperature is lower than the exhaust gas reference temperature, and the second reference temperature is higher than the exhaust gas reference temperature (first reference temperature < exhaust gas reference temperature < second reference temperature).

[0118] like Figure 10 As shown, the control unit 11 first determines whether the temperature of the refrigerant (cooling water temperature) is below the refrigerant reference temperature (S1). If the cooling water temperature is higher than the refrigerant reference temperature (S1: No), the control unit 11 determines whether the temperature of the exhaust gas (exhaust gas temperature) is below the exhaust gas reference temperature (S2). If the exhaust gas temperature is higher than the exhaust gas reference temperature (S2: No), the control unit 11 performs EGR gas recirculation in cooling mode (S3).

[0119] Then, the control unit 11 determines whether the flow of EGR gas is stable (S4). If the temperature of the EGR gas remains below the EGR gas reference temperature for a certain period of time (S4: Yes), the control unit 11 performs EGR gas recirculation in bypass mode (S8). If the temperature of the EGR gas does not remain below the EGR gas reference temperature for a certain period of time (S4: No), the control unit 11 performs EGR gas recirculation in cooling mode (S5).

[0120] Additionally, if the cooling water temperature is below the refrigerant reference temperature (S1: Yes), the control unit 11 determines whether the exhaust gas temperature is below the first reference temperature (S6). If the exhaust gas temperature is above the first reference temperature (S6: No), the control unit 11 determines whether the exhaust gas temperature is below the second reference temperature (S7). If the exhaust gas temperature is above the second reference temperature (S7: No), the control unit 11 moves the process to step S3 (recirculating the EGR gas in cooling mode).

[0121] On the other hand, if the exhaust gas temperature is below the second reference temperature (S7: Yes), the control unit 11 moves the processing to step S8 (recirculating the EGR gas in bypass mode). Additionally, if the exhaust gas temperature is below the first reference temperature (S6: Yes), the control unit 11 stops the recirculation of the EGR gas (S9).

[0122] During normal operation of the engine body 2, the control unit 11 repeatedly executes the above-described steps S1 to S9. However, Figure 10 The flowchart shown is just an example; processes can be added or omitted as appropriate, and the order of processes can be changed as appropriate.

[0123] Figure 11 This is a flowchart illustrating an example of the process involved in the control method of the exhaust gas recirculation system 4 executed in the control unit 11, particularly the operation involved in the regeneration of the exhaust gas purification device 53. Here, the first reference temperature is lower than the second reference temperature (first reference temperature < second reference temperature).

[0124] like Figure 11 As shown, the control unit 11 first determines whether the temperature of the exhaust gas (exhaust gas temperature) is below a first reference temperature (S11). If the exhaust gas temperature is below the first reference temperature (S11: Yes), the control unit 11 stops the EGR gas recirculation (S15). If the exhaust gas temperature is above the first reference temperature (S11: No), the control unit 11 determines whether the temperature of the exhaust gas (exhaust gas temperature) is below a second reference temperature (S12). If the exhaust gas temperature is above the second reference temperature (S12: No), the control unit 11 stops the EGR gas recirculation (S15).

[0125] If the exhaust gas temperature is below the second reference temperature (S12: Yes), the control unit 11 determines whether there is post-injection during the regeneration of the exhaust gas purification device 53 (S13). If the regeneration mode of the exhaust gas purification device 53 is an active (forced) regeneration mode accompanied by post-injection, the control unit 11 determines that there is post-injection (S13: Yes) and stops the backflow of EGR gas (S15).

[0126] On the other hand, if the regeneration mode of the exhaust gas purification device 53 is a passive regeneration mode without post-injection, the control unit 11 determines that there is no post-injection (S13: No) and performs EGR gas recirculation in bypass mode (S14).

[0127] During the regeneration of the exhaust gas purification device 53, the control unit 11 repeats the above steps S11 to S15. However, Figure 11 The flowchart shown is just an example; processes can be added or omitted as appropriate, and the order of processes can be changed as appropriate.

[0128] [3] Details of the post-processing system

[0129] Next, refer to Figure 6 as well as Figures 12-18 Details of the post-processing system 5 involved in this embodiment will be described.

[0130] like Figure 6 As shown, in addition to the first SCR device 51, the second SCR device 52, and the exhaust gas purification device 53, the aftertreatment system 5 also includes a first ASC (Ammonia slip catalyst) device 54, a second ASC device 55, a first reducing agent supply device 56, and a second reducing agent supply device 57. Here, the control unit 11 is capable of controlling the aftertreatment system 5, and specifically the first reducing agent supply device 56 and the second reducing agent supply device 57, and is therefore considered a component of the aftertreatment system 5.

[0131] The components of the aftertreatment system 5 described above are arranged in the exhaust path 28. In particular, the first SCR device 51, the first ASC device 54, the exhaust gas purification device 53, the second SCR device 52, and the second ASC device 55 are connected in series from the upstream side of the exhaust gas flow direction in the exhaust path 28. That is, the exhaust gas discharged from the engine body 2 into the exhaust path 28 passes through the first SCR device 51, the first ASC device 54, the exhaust gas purification device 53, the second SCR device 52, and the second ASC device 55 in sequence. Furthermore, the oxidation catalyst 531 and the particulate filter 532 of the exhaust gas purification device 53 are connected such that the oxidation catalyst 531 is located upstream of the exhaust gas flow direction in the exhaust path 28 and the particulate filter 532 is located downstream.

[0132] Thus, the exhaust gas through exhaust path 28 sequentially passes through the first SCR device 51, the first ASC device 54, the oxidation catalyst 531, the particulate filter 532, the second SCR device 52, and the second ASC device 55. In the aftertreatment system 5, relative to the exhaust gas purification device 53 (oxidation catalyst 531 and particulate filter 532), there is a group of the first SCR device 51 and the first ASC device 54 on the upstream side (in the direction of exhaust gas flow), and a group of the second SCR device 52 and the second ASC device 55 on the downstream side.

[0133] The first SCR device 51 and the first ASC device 54 are housed in the first SCR housing 501, and the exhaust gas purification device 53, the second SCR device 52, and the second ASC device 55 are housed in the second SCR housing 502. The first SCR housing 501 and the second SCR housing 502 are generally cylindrical housings (frames) and are inserted into the exhaust path 28.

[0134] Specifically, the exhaust path 28 includes a connecting path 71, an intermediate path 72, and a downstream path 73. The connecting path 71 connects the exhaust port 202 to the first SCR housing 501. The intermediate path 72 connects the first SCR housing 501 to the second SCR housing 502. The downstream path 73 connects to the second SCR housing 502 downstream of the exhaust gas flow direction. In other words, the connecting path 71, the first SCR housing 501, the intermediate path 72, the second SCR housing 502, and the downstream path 73 are connected in series from the upstream side of the exhaust gas flow direction.

[0135] Within the first SCR housing 501, the first SCR device 51 and the first ASC device 54 are sequentially connected in series and housed from the upstream side of the exhaust gas flow direction (i.e., the side of connection path 71). Within the second SCR housing 502, the oxidation catalyst 531, the particulate filter 532, the second SCR device 52, and the second ASC device 55 are sequentially connected in series and housed from the upstream side of the exhaust gas flow direction (i.e., the side of intermediate path 72).

[0136] Here, the first reducing agent supply device 56 and the second reducing agent supply device 57 supply reducing agent (urea as an example in this embodiment) to the first SCR device 51 and the second SCR device 52, respectively. Specifically, the first reducing agent supply device 56 sprays reducing agent into the connecting path 71 in the exhaust path 28, thereby supplying reducing agent to the first SCR device 51. The second reducing agent supply device 57 sprays reducing agent into the position between the particulate filter 532 and the second SCR device 52 inside the second SCR housing 502, thereby supplying reducing agent to the second SCR device 52. The first reducing agent supply device 56 is also simply referred to as "reducing agent supply device 56".

[0137] Thus, the first reducing agent supply device 56 is located upstream of the first SCR device 51 in the direction of exhaust gas flow. The first reducing agent supply device 56 injects urea, acting as a reducing agent, into the exhaust path 28. The first SCR device 51 reduces nitrogen oxides in the exhaust gas to nitrogen by generating ammonia from the hydrolysis of urea by the exhaust heat of the engine body 2. The second reducing agent supply device 57 is located upstream of the second SCR device 52 in the direction of exhaust gas flow. The second reducing agent supply device 57 injects urea, acting as a reducing agent, into the exhaust path 28. The second SCR device 52 reduces nitrogen oxides in the exhaust gas to nitrogen by generating ammonia from the hydrolysis of urea by the exhaust heat of the engine body 2.

[0138] As explained above, the aftertreatment system 5 according to this embodiment is configured as a dual-supply system that connects two SCRs (a first SCR device 51 and a second SCR device 52) in series and supplies a reducing agent (urea) to each of the two SCRs. Therefore, the aftertreatment system 5 efficiently decomposes nitrogen oxides depending on the conditions; for example, under light load conditions with low exhaust gas temperature, the first SCR device 51, located closer to the engine block 2, mainly operates, while under heavy load conditions with high exhaust gas temperature, the second SCR device 52 mainly operates. Thus, the aftertreatment system 5 can significantly reduce nitrogen oxides in the exhaust gas.

[0139] The carriers of the first SCR device 51 and the second SCR device 52 can be the same or different. Metals (e.g., stainless steel), ceramics (e.g., silicon carbide or cordierite), etc., can be used as carriers. Each of the first SCR device 51 and the second SCR device 52 uses a catalyst to convert nitrogen oxides (NOx) in the exhaust gas into nitrogen molecules (N2) and water (H2O), thereby reducing nitrogen oxides in the exhaust gas.

[0140] Furthermore, each of the first ASC device 54 and the second ASC device 55 is an example of a decomposition catalyst, which is a catalyst for oxidizing and decomposing the unconsumed ammonia in the first SCR device 51 and the second SCR device 52. This prevents ammonia from being released into the atmosphere.

[0141] In addition, the exhaust gas purification device 53 decomposes particulate matter in the exhaust gas using the oxidation catalyst 531 and captures it using the particulate filter 532. Here, if the particulate matter captured by the particulate filter 532 remains in its original state, it will cause blockage of the particulate filter 532. Therefore, the particulate filter 532 needs to be regenerated in the exhaust gas purification device 53.

[0142] As described above, the regeneration modes of the exhaust gas purification device 53 include an active (forced) regeneration mode with post-injection and a passive regeneration mode without post-injection. In the active regeneration mode, unburned fuel is forcibly introduced into the oxidation catalyst 531 through a post-injection that delays the main combustion injection period, thereby forcibly raising the temperature of the exhaust gas and causing the particulate matter accumulated in the particulate trap 532 to burn. In the passive regeneration mode, regeneration is performed using catalyst-based oxidation, without utilizing heat from an external heat source, and is referred to as a "continuous regeneration mode" or "self-regeneration mode."

[0143] However, the aftertreatment system 5 according to this embodiment includes: an exhaust gas purification device 53, a (first) SCR device 51, and a connection path 71. The exhaust gas purification device 53 captures particulate matter in the exhaust gas discharged from the engine body 2. The SCR device 51 is located between the exhaust port 202 of the engine body 2 and the exhaust gas purification device 53. The connection path 71 connects the exhaust port 202 to the SCR device 51. Here, as Figures 12-14 As shown, the connecting path 71 has a first path 711, a second path 712, and a connecting portion 713. The first path 711 and the second path 712 have lengths in the directions in which they intersect. The connecting portion 713 connects the first path 711 and the second path 712.

[0144] That is, the connecting path 71 in the exhaust path 28, located between the exhaust port 202 and the (first) SCR device 51, is not a straight line, but includes a first path 711 and a second path 712 with lengths in mutually intersecting directions. The connecting portion 713 that connects the first path 711 and the second path 712 is a bend (including a buckling portion and a bending portion).

[0145] Therefore, on the upstream side (exhaust port 202 side) of the exhaust gas flow direction when viewed from the SCR device 51, the temperature of the wall (pipe wall) of the connection path 71 easily rises due to the heat of the exhaust gas (heat dissipation). As a result, even if the connection path 71 from the exhaust port 202 of the engine body 2 to the SCR device 51 is shortened, the reducing agent easily and sufficiently decomposes, and the purification performance of the exhaust gas in the SCR device 51 is not easily reduced. In addition, compared with the case of lengthening the connection path 71, shortening the connection path 71 allows the SCR device 51 to heat up earlier, for example, after the engine body 2 is started, thus shortening the time required for the SCR device 51 to reach the activation temperature. Therefore, the purification performance of the exhaust gas immediately after the engine body 2 is started is not easily reduced.

[0146] In summary, the connecting portion 713 of the connecting path 71 is the part that changes the direction of the exhaust gas flow from the intersecting first directions (the length direction of the first path 711) to the second direction (the length direction of the second path 712). In this embodiment, as an example, such as... Figures 12-14 As shown, the first direction (the length direction of the first path 711) is the vertical direction D2, and the second direction (the length direction of the second path 712) is the output shaft direction D1. That is, the exhaust gas passing through the connecting path 71 travels along the vertical direction D2 (from bottom to top) through the first path 711, and after its direction is changed in the connecting part 713, it travels along the output shaft direction D1 (from rear to front) through the second path 712. At this time, the exhaust gas collides with the wall (pipe wall) of the connecting path 71, therefore the temperature of the wall (pipe wall) of the connecting path 71 easily rises.

[0147] Alternatively, for example, the connection path 71 could be shortened by placing the mixer or evaporator immediately before the SCR device 51. However, in this case, there is a possibility of fuel efficiency deterioration due to increased pressure loss, and there is also a risk of breakage, which would reduce the reliability of the aftertreatment system 5. In contrast, in this embodiment, the connection path 71 can be shortened even without a mixer or evaporator, thus suppressing such adverse conditions.

[0148] In this embodiment, a booster compressor 6 is further disposed upstream of the exhaust gas flow direction (exhaust port 202 side) when viewed from the connection path 71. Therefore, the exhaust gas passing through the booster compressor 6 is introduced into the connection path 71. Here, as... Figure 12 As shown, the booster compressor 6 is located in front of the first path 711. The exhaust gas passing through the booster compressor 6 from front to back passes through the first path 711 from bottom to top, and then passes through the second path 712 from back to front, thus being introduced into the SCR device 51. In this way, the connecting path 71 is arranged immediately after the booster compressor 6, so that the exhaust gas can easily collide with the wall (pipe wall) of the connecting path 71, which can easily cause the wall temperature to rise.

[0149] Here, the connecting path 71 also has a straight section located between the connecting part 713 and the SCR device 51, allowing exhaust gas to pass through. In this embodiment, the second path 712, which has a length in the output shaft direction D1, is straight, and therefore the second path 712 is an example of a straight section. With such a straight section (second path 712), the exhaust gas passing through the connecting part 713 can flow smoothly to the SCR device 51.

[0150] In addition, the aftertreatment system 5 according to this embodiment also includes a (first) reducing agent supply device 56 for supplying reducing agent to the interior of the connection portion 713. That is, reducing agent is supplied from the reducing agent supply device 56 to the connection portion 713 located upstream of the exhaust gas flow direction when viewed from the SCR device 51.

[0151] Specifically, such as Figure 13 As shown, the reducing agent supply device 56 is disposed on the outside of the connecting part 713 in the connecting path 71, and sprays the reducing agent (urea) into the connecting part 713 through the hole formed in the connecting path 71. Figure 13 yes Figure 12 A magnified view of region Z1, with thick arrows schematically illustrating the flow of exhaust gas. Furthermore, in... Figure 13 The diagram schematically shows a droplet X1 of reducing agent (urea) and ammonia gas X2.

[0152] That is, the reducing agent supply device 56 sprays the reducing agent into the connecting part 713 in the connecting path 71, so that the reducing agent droplets X1 can easily collide with the wall (pipe wall) of the connecting part 713 after being heated by the exhaust gas. As a result, the decomposition of the reducing agent is promoted, and the generation of ammonia X2 is promoted.

[0153] Furthermore, the reducing agent supply device 56 sprays the reducing agent downstream of the exhaust gas flow direction. In this embodiment, the reducing agent supply device 56 sprays the reducing agent at the connection portion 713 towards the SCR device 51 side, which is downstream of the exhaust gas flow direction. This allows the reducing agent droplets X1 and ammonia X2 to be transported along with the exhaust gas towards the SCR device 51 side, facilitating the supply of the reducing agent to the SCR device 51.

[0154] The connection path 71 has a stirring section in the connecting part 713 for stirring the exhaust gas. In this embodiment, the wall surface (pipe wall) of the connecting part 713 functions as the stirring section for stirring the exhaust gas. As a result, the exhaust gas actively heats the wall surface (pipe wall) of the connecting part 713, and the temperature of the wall surface (pipe wall) of the connecting part 713 easily rises.

[0155] In addition, in this embodiment, such as Figure 14 As shown, connection path 71 is connected to SCR device 51 from a direction intersecting the direction of the exhaust gas flow in SCR device 51. Here, the direction of the exhaust gas flow in SCR device 51 is the width direction D3 (from left to right), and connection path 71 is connected to SCR device 51 from the output shaft direction D1 (behind it), which intersects (orthogonally) with it. This facilitates the action of the reducing agent (ammonia X2) introduced into SCR device 51 from connection path 71 on SCR device 51.

[0156] Furthermore, the connection path 71 discharges the exhaust gas introduced from one side to the same side. In this embodiment, exhaust gas is introduced from the front side of the output shaft direction D1 relative to the connection path 71 (first path 711), and exhaust gas is discharged from the connection path 71 (second path 712) to the front side of the output shaft direction D1. As a result, the exhaust gas is prone to colliding with the wall (pipe wall) of the connection path 71, which easily causes the wall temperature to rise.

[0157] In addition, such as Figure 15 As shown, the reducing agent supply device 56 can also spray the reducing agent at the connection 713 upstream of the flow direction of the exhaust gas. That is, the reducing agent supply device 56 sprays the reducing agent at the connection 713 towards the first path 711, which is upstream of the flow direction of the exhaust gas. As a result, the reducing agent droplets X1 and ammonia X2 can be transported along with the exhaust gas toward the SCR device 51, making it easier to supply the reducing agent to the SCR device 51.

[0158] However, the aftertreatment system 5 according to this embodiment includes: a first SCR device 51, a second SCR device 52, a first reducing agent supply device 56, a second reducing agent supply device 57, and a control unit 11. The first SCR device 51 is located on the exhaust path 28 through which exhaust gas discharged from the engine body 2 passes. The second SCR device 52 is located on the exhaust path 28 and downstream of the first SCR device in the direction of exhaust gas flow. The first reducing agent supply device 56 supplies reducing agent to the first SCR device 51. The second reducing agent supply device 57 supplies reducing agent to the second SCR device 52. The control unit 11 individually controls the amount of reducing agent supplied to each of the first reducing agent supply device 56 and the second reducing agent supply device 57.

[0159] In other words, the control method of the post-processing system 5 according to this embodiment can be regarded as a control method of the post-processing system 5 comprising a first SCR device 51, a second SCR device 52, a first reducing agent supply device 56, and a second reducing agent supply device 57. This control method includes: individually controlling the amount of reducing agent supplied to each of the first reducing agent supply device 56 and the second reducing agent supply device 57.

[0160] In summary, in the dual-supply aftertreatment system 5 configured to supply a reducing agent (urea) to each of the first SCR unit 51 and the second SCR unit 52, the amount of reducing agent supplied to the first SCR unit 51 and the second SCR unit 52 is controlled individually. For example, in order to perform passive regeneration (self-regeneration) of the exhaust gas purification device 53, nitrogen dioxide (NO2) obtained by oxidizing the nitric oxide (NO) flowing into the exhaust gas purification device 53 needs to be supplied to the particulate filter 532. In the aftertreatment system 5 according to this embodiment, the amount of reducing agent supplied can be limited only to the first reducing agent supply device 56 or the second reducing agent supply device 57 as needed, thereby adjusting the purification capacity of nitrogen oxides in each of the first SCR unit 51 and the second SCR unit 52.

[0161] Therefore, according to the post-treatment system 5, for example, the purification capacity of nitric oxide is suppressed only for the first SCR device 51 located upstream of the exhaust gas purification device 53, thereby maintaining the amount of nitric oxide flowing into the exhaust gas purification device 53 to ensure the regeneration capacity of the exhaust gas purification device 53. As a result, the post-treatment system 5 according to this embodiment has the advantage that the purification performance of exhaust gas is not easily reduced.

[0162] Specifically, such as Figure 16As shown, the post-treatment system 5 controls each of the first reducing agent supply device 56 and the second reducing agent supply device 57 individually via the control unit 11. Here, the control unit 11 can control the supply amount (injection amount) of the reducing agent in each of the first reducing agent supply device 56 and the second reducing agent supply device 57 within the range of 0% to 100%.

[0163] In addition, Figure 16 In the example, the post-processing system 5 includes a first mixer 591 and a second mixer 592. The first mixer 591 is disposed immediately upstream of the first SCR device 51, and the second mixer 592 is disposed immediately upstream of the second SCR device 52. However, the first mixer 591 and the second mixer 592 are not necessary and can be omitted appropriately.

[0164] More specifically, in this embodiment, the aftertreatment system 5 includes an exhaust gas purification device 53 for capturing particulate matter in the exhaust gas. The exhaust gas purification device 53 is located between the first SCR device 51 and the second SCR device 52 in the exhaust path 28. The control unit 11 controls the amount of reducing agent supplied to each of the first reducing agent supply device 56 and the second reducing agent supply device 57 so that the regeneration capacity of the exhaust gas purification device 53 is above a predetermined value.

[0165] In this way, by adjusting the amount of reducing agent supplied to each of the first reducing agent supply device 56 and the second reducing agent supply device 57, based on the regeneration capacity of the exhaust gas purification device 53, the amount of nitric oxide flowing into the exhaust gas purification device 53 can be easily maintained to ensure the regeneration capacity of the exhaust gas purification device 53. As a result, according to the post-treatment system 5 of this embodiment, the purification performance of the exhaust gas is not easily reduced.

[0166] Here, the control unit 11 controls the amount of reducing agent supplied to each of the first reducing agent supply device 56 and the second reducing agent supply device 57 based on whether the regeneration mode of the exhaust gas purification device 53 is passive or active regeneration mode. That is, as described above, when the exhaust gas purification device 53 is regenerated in passive regeneration mode, nitrogen dioxide (NO2), obtained by oxidizing the nitric oxide (NO) flowing into the exhaust gas purification device 53, needs to be supplied to the particulate filter 532. In contrast, in active regeneration mode, post-injection is performed to supply oxygen (O2) from the exhaust gas to the particulate filter 532 and burn the particulate matter. Therefore, in active regeneration mode, it is not necessary to supply nitrogen dioxide to the particulate filter 532.

[0167] Furthermore, the supply of reducing agent to each of the first reducing agent supply device 56 and the second reducing agent supply device 57 is controlled according to whether the regeneration mode of the exhaust gas purification device 53 is passive or active regeneration mode, thus avoiding an excessive reduction in the purification capacity of the first SCR device 51. In summary, in passive regeneration mode, for example, by suppressing the supply of reducing agent to the first reducing agent supply device 56 to a lower level, the purification capacity of nitrogen oxides in the first SCR device 51 is suppressed to a lower level, thereby maintaining the amount of nitric oxide flowing into the exhaust gas purification device 53. On the other hand, in active regeneration mode, for example, by increasing the supply of reducing agent to the first reducing agent supply device 56, the purification capacity of nitrogen oxides in the first SCR device 51 can be improved. In either case, the regeneration capacity of the exhaust gas purification device 53 can be easily ensured.

[0168] Furthermore, in this embodiment, the control unit 11 controls the amount of reductant supplied to each of the first reductant supply device 56 and the second reductant supply device 57 based on the catalyst temperature of each of the first SCR device 51 and the second SCR device 52. For example, when the catalyst temperature of the first SCR device 51 is low, sufficient purification capacity of nitrogen oxides in the first SCR device 51 cannot be expected, so the control unit 11 suppresses the amount of reductant supplied to the first SCR device 51 by the first reductant supply device 56 to be less. Similarly, for example, when the catalyst temperature of the second SCR device 52 is low, sufficient purification capacity of nitrogen oxides in the second SCR device 52 cannot be expected, so the control unit 11 suppresses the amount of reductant supplied to the second SCR device 52 by the second reductant supply device 57 to be less. As a result, the consumption of reductant can be suppressed.

[0169] Specifically, such as Figure 16 As shown, the post-processing system 5 includes a first temperature sensor 121 and a second temperature sensor 122 included in the sensor 12. The first temperature sensor 121 measures the catalyst temperature of the first SCR unit 51, and the second temperature sensor 122 measures the catalyst temperature of the second SCR unit 52. The measurement results of the first temperature sensor 121 and the second temperature sensor 122 are output to the control unit 11. Based on the measurement results of the first temperature sensor 121 and the second temperature sensor 122, the control unit 11 controls the amount of reducing agent supplied to each of the first reducing agent supply device 56 and the second reducing agent supply device 57.

[0170] In this embodiment, in particular, if the catalyst temperature of both the first SCR device 51 and the second SCR device 52 is above the activation temperature, and the exhaust gas purification device 53 is regenerating in active regeneration mode, the control unit 11 ensures that the amount of reducing agent supplied by the first reducing agent supply device 56 is greater than the amount of reducing agent supplied by the second reducing agent supply device 57. That is, even if both the first SCR device 51 and the second SCR device 52 are capable of purifying nitrogen oxides, if the exhaust gas purification device 53 is regenerating in active regeneration mode, the first SCR device 51 primarily purifies nitrogen oxides compared to the second SCR device 52. In other words, in active regeneration mode where nitric oxide does not need to be introduced into the exhaust gas purification device 53, the nitrogen oxide purification capacity of the first SCR device 51 can be higher than that of the second SCR device 52, thereby ensuring sufficient nitrogen oxide purification capacity.

[0171] Furthermore, if the catalyst temperatures of both the first SCR device 51 and the second SCR device 52 are above their activation temperatures, the control unit 11 controls the amount of reducing agent supplied to each of the first reducing agent supply device 56 and the second reducing agent supply device 57 based on the inlet temperature of the exhaust gas purification device 53. For example, the inlet temperature of the exhaust gas purification device 53 is detected based on the temperature of the exhaust gas passing through the intermediate path 72 as measured by the temperature sensor included in the sensor 12.

[0172] If the inlet temperature of the exhaust gas purification device 53 is too high, the amount of nitrogen dioxide generated from nitric oxide flowing into the exhaust gas purification device 53 will decrease, and therefore sufficient regeneration capacity in the exhaust gas purification device 53 cannot be expected. Therefore, for example, when the inlet temperature of the exhaust gas purification device 53 is above a predetermined temperature, the amount of reducing agent supplied to the first reducing agent supply device 56 can be increased, thereby improving the purification capacity of nitrogen oxides in the first SCR device 51.

[0173] Specifically, if the catalyst temperatures of both the first SCR device 51 and the second SCR device 52 are above their activation temperatures, and the inlet temperature of the exhaust gas purification device 53 is above a predetermined temperature, then the control unit 11 ensures that the amount of reducing agent supplied by the first reducing agent supply device 56 is greater than the amount of reducing agent supplied by the second reducing agent supply device 57. That is, even if both the first SCR device 51 and the second SCR device 52 are capable of purifying nitrogen oxides, if the generation of nitrogen dioxide is reduced, then the first SCR device 51 will primarily purify nitrogen oxides compared to the second SCR device 52. In other words, even when sufficient regeneration capacity in the exhaust gas purification device 53 cannot be expected, the purification capacity of nitrogen oxides in the first SCR device 51 can be higher than that in the second SCR device 52, thereby ensuring sufficient nitrogen oxide purification capacity.

[0174] Furthermore, if the catalyst temperatures of both the first SCR device 51 and the second SCR device 52 are above their activation temperatures, and the inlet temperature of the exhaust gas purification device 53 is below a predetermined temperature, the control unit 11 ensures that the amount of reducing agent supplied by the second reducing agent supply device 57 is greater than the amount of reducing agent supplied by the first reducing agent supply device 56. That is, if both the first SCR device 51 and the second SCR device 52 are capable of purifying nitrogen oxides and nitrogen dioxide is sufficiently generated, then the second SCR device 52 primarily purifies nitrogen oxides compared to the first SCR device 51. In other words, under conditions where sufficient regeneration capacity can be expected in the exhaust gas purification device 53, the purification capacity of nitrogen oxides in the first SCR device 51 can be suppressed to be lower than that in the second SCR device 52, thereby maintaining the amount of nitric oxide flowing into the exhaust gas purification device 53.

[0175] Furthermore, when the catalyst temperature of only the first SCR unit 51 is above the activation temperature in both the first SCR unit 51 and the second SCR unit 52, the control unit 11 supplies reducing agent only from the first reducing agent supply device 56 of the first reducing agent supply device 56 and the second reducing agent supply device 57. In other words, if the catalyst temperature of the second SCR unit 52 is below the activation temperature, sufficient purification capacity of nitrogen oxides in the second SCR unit 52 cannot be expected, therefore the control unit 11 stops the supply of reducing agent to the second SCR unit 52 from the second reducing agent supply device 57. This suppresses the consumption of reducing agent.

[0176] Furthermore, when the catalyst temperature of only the second SCR unit 52 is above the activation temperature in both the first SCR unit 51 and the second SCR unit 52, the control unit 11 supplies reducing agent only from the second reducing agent supply unit 57 of the first reducing agent supply unit 56 and the second reducing agent supply unit 57. In other words, if the catalyst temperature of the first SCR unit 51 is below the activation temperature, sufficient purification capacity of nitrogen oxides in the first SCR unit 51 cannot be expected, therefore the control unit 11 stops the supply of reducing agent to the first SCR unit 51 from the first reducing agent supply unit 56. This suppresses the consumption of reducing agent.

[0177] Figure 17 The operation of the post-processing system 5 according to this embodiment under various conditions is illustrated. Figure 17 In this context, "DM" is an abbreviation for "Dosing Module," "DM1" represents the first reducing agent supply device 56, and "DM2" represents the second reducing agent supply device 57.

[0178] First, examples 1 through 5 will be described in the case where the exhaust gas purification device 53 is not regenerated (DPF regeneration: none). In example 1, where the catalyst temperature of both the first SCR device 51 and the second SCR device 52 is lower than the activation temperature, both the first reducing agent supply device 56 and the second reducing agent supply device 57 stop supplying reducing agent (reducing agent control: no injection).

[0179] In Example 2, where only the catalyst temperature of the first SCR unit 51 is above the activation temperature, only the first reducing agent supply device 56 supplies the reducing agent (reducing agent control: DM1), and the first SCR unit 51 purifies nitrogen oxides. In Example 3, where only the catalyst temperature of the second SCR unit 52 is above the activation temperature, only the second reducing agent supply device 57 supplies the reducing agent (reducing agent control: DM2), and the second SCR unit 52 purifies nitrogen oxides.

[0180] Furthermore, in Examples 4 and 5, where the catalyst temperatures of the first SCR unit 51 and the second SCR unit 52 are above their activation temperatures, the operation varies depending on the inlet temperature (DOC temperature) of the exhaust gas purification unit 53. That is, in Example 4, where the inlet temperature of the exhaust gas purification unit 53 is above a specified temperature, the amount of reductant supplied by the first reductant supply unit 56 is greater than the amount of reductant supplied by the second reductant supply unit 57 (reductant control: DM1 (main) + DM2), and the first SCR unit 51 is primarily responsible for purifying nitrogen oxides. In Example 5, where the inlet temperature of the exhaust gas purification unit 53 is below a specified temperature, the amount of reductant supplied by the second reductant supply unit 57 is greater than the amount of reductant supplied by the first reductant supply unit 56 (reductant control: DM1 + ​​DM2 (main)), and the second SCR unit 52 is primarily responsible for purifying nitrogen oxides.

[0181] Next, Examples 6 to 9 will be described when the exhaust gas purification device 53 is being regenerated (DPF regeneration: present). In Example 6, where the catalyst temperature of both the first SCR device 51 and the second SCR device 52 is lower than the activation temperature, both the first reducing agent supply device 56 and the second reducing agent supply device 57 stop supplying reducing agent (reducing agent control: no injection).

[0182] In Example 7, where only the catalyst temperature of the first SCR unit 51 is above the activation temperature, only the first reducing agent supply device 56 supplies the reducing agent (reducing agent control: DM1), and the first SCR unit 51 purifies nitrogen oxides. In Example 8, where only the catalyst temperature of the second SCR unit 52 is above the activation temperature, only the second reducing agent supply device 57 supplies the reducing agent (reducing agent control: DM2), and the second SCR unit 52 purifies nitrogen oxides.

[0183] In Example 9, where the catalyst temperatures of the first SCR unit 51 and the second SCR unit 52 are above their activation temperatures, the inlet temperature of the unrelated exhaust gas purification device 53 operates in the same manner as in Example 4. That is, in Example 9, the amount of reducing agent supplied by the first reducing agent supply device 56 is greater than the amount of reducing agent supplied by the second reducing agent supply device 57 (reducing agent control: DM1 (main) + DM2), with the first SCR unit 51 being the primary source for nitrogen oxide purification.

[0184] Figure 18 This is a flowchart illustrating an example of the processing involved in the control method of the post-processing system 5 executed in the control unit 11.

[0185] like Figure 18 As shown, the control unit 11 first determines whether the catalyst temperature of the first SCR device 51 is above the activation temperature (S21). If the temperature of the first SCR device 51 is above the activation temperature (S21: Yes), the control unit 11 then determines whether the catalyst temperature of the second SCR device 52 is above the activation temperature (S22). Here, if the temperature of the second SCR device 52 is below the activation temperature (S22: No), the control unit 11 only causes the first reducing agent supply device 56 to supply reducing agent (S27).

[0186] On the other hand, if the temperature of the first SCR device 51 is lower than the activation temperature (S21: No), the control unit 11 also determines whether the catalyst temperature of the second SCR device 52 is above the activation temperature (S28). Here, if the temperature of the second SCR device 52 is above the activation temperature (S28: Yes), the control unit 11 only supplies the reductant to the second reductant supply device 57 (S29). Alternatively, if the temperature of the second SCR device 52 is lower than the activation temperature (S28: No), the control unit 11 prevents both the first reductant supply device 56 and the second reductant supply device 57 from supplying the reductant (S30).

[0187] In step S22, if the temperature of the second SCR device 52 is above the activation temperature (S22: Yes), the control unit 11 determines whether the exhaust gas purification device 53 is regenerating in active regeneration mode (S23). If the exhaust gas purification device 53 is regenerating in active regeneration mode (S23: Yes), the control unit 11 increases the amount of reducing agent supplied by the first reducing agent supply device 56 to more than the amount of reducing agent supplied by the second reducing agent supply device 57 (S25). As a result, the first SCR device 51 actively purifies nitrogen oxides.

[0188] Furthermore, if the exhaust gas purification device 53 is not regenerating in active regeneration mode (S23: No), the control unit 11 determines whether the inlet temperature of the exhaust gas purification device 53 is above a predetermined temperature (S24). If the inlet temperature of the exhaust gas purification device 53 is above the predetermined temperature (S24: Yes), the control unit 11 increases the amount of reducing agent supplied by the first reducing agent supply device 56 by more than the amount of reducing agent supplied by the second reducing agent supply device 57 (S25). If the inlet temperature of the exhaust gas purification device 53 is below the predetermined temperature (S24: No), the control unit 11 increases the amount of reducing agent supplied by the second reducing agent supply device 57 by more than the amount of reducing agent supplied by the first reducing agent supply device 56 (S26). Thus, the first SCR device 51 passively purifies nitrogen oxides.

[0189] More specifically, in step S26, the control unit 11 calculates a target value for the overall purification rate of the first SCR device 51 and the second SCR device 52 based on the catalyst temperatures, exhaust gas flow rates, ammonia adsorption amounts, and nitrogen oxide inflow rates of each catalyst in the first SCR device 51 and the second SCR device 52. Furthermore, the control unit 11 calculates the maximum purification rate of the second SCR device 52, subtracts the purification rate of the second SCR device 52 from the target value of the overall purification rate, and compensates for the difference using the purification rate of the first SCR device 51. In other words, the value obtained by subtracting the purification rate of the second SCR device 52 from the target value of the overall purification rate becomes the purification rate of the first SCR device 51. The control unit 11 determines the amount of reducing agent supplied to the first reducing agent supply device 56 so as not to exceed the calculated purification rate of the first SCR device 51. If the calculated purification rate of the first SCR device 51 is "0%", the control unit 11 stops the supply of reducing agent to the first reducing agent supply device 56.

[0190] The control unit 11 repeats the processing of steps S21 to S30 described above. However, Figure 18 The flowchart shown is just an example; processes can be added or omitted as appropriate, and the order of processes can be changed as appropriate.

[0191] However, in the aftertreatment system 5 according to this embodiment, urea, which is a reducing agent injected into the exhaust path 28, sometimes precipitates as a solid substance and becomes deposited. If the deposits accumulate in the exhaust path 28, there is a risk of pressure loss, etc. In the second SCR device 52, an oxidation catalyst 531 is arranged upstream of the exhaust gas flow direction, so the deposits can be removed by burning fuel with the oxidation catalyst 531 and using the high-temperature exhaust gas to decompose and evaporate the deposits. On the other hand, in the first SCR device 51, an oxidation catalyst 531 cannot be arranged upstream of the exhaust gas flow direction, so it is difficult to remove the deposits.

[0192] Therefore, in this embodiment, in order to fundamentally suppress the formation of deposits in the first SCR device 51, the control unit 11 determines the upper limit of the amount of reducing agent supplied to the first reducing agent supply device 56 based on the temperature and flow rate of the exhaust gas. Here, the temperature of the exhaust gas can be measured near the exhaust port 202 of the exhaust manifold 26 by a temperature sensor included in the sensor 12, or it can be inferred from, for example, the outside air temperature or the intake air temperature. In addition, the flow rate of the exhaust gas can be measured by a flow sensor, or it can be inferred from, for example, the engine speed or load of the engine body 2.

[0193] In summary, the formation of deposits in the first SCR unit 51 largely depends on the wall temperature of the exhaust path 28, which is impacted by urea as a reducing agent. Furthermore, as the urea injection rate increases, the wall temperature decreases due to the latent heat of vaporization during the collision of urea with the wall. For example, if the wall temperature falls below 195°C, deposits are more likely to form. Therefore, when the exhaust gas temperature is high and the wall temperature is sufficiently high, even increasing the urea injection rate does not easily lead to deposit formation, thus allowing for a larger upper limit on the amount of reducing agent supplied to the first reducing agent supply device 56.

[0194] In this way, instead of simply suppressing the supply of reducing agent, the upper limit of the supply of reducing agent to the first reducing agent supply device 56 is determined based on the temperature and flow rate of the exhaust gas. This allows for an increase in the supply of reducing agent to the first reducing agent supply device 56 when the exhaust gas temperature is sufficiently high and deposits are unlikely to form. Therefore, it avoids excessive restriction of the supply of reducing agent to the first reducing agent supply device 56, which could reduce the purification rate of nitrogen oxides in the first SCR device 51.

[0195] Furthermore, when the supply of reducing agent to the first reducing agent supply device 56 is limited by an upper limit, the control unit 11 increases the supply of reducing agent to the second reducing agent supply device 57 by a compensation amount equivalent to the limited amount. In other words, the amount by which the reduction in the nitrogen oxide purification rate in the first SCR device 51 due to the limitation on the supply of reducing agent to the first reducing agent supply device 56 can be compensated by the second SCR device 52 by increasing the supply of reducing agent to the second reducing agent supply device 57. As a result, the desired nitrogen oxide purification rate can be achieved.

[0196] [4] Modified Examples

[0197] Hereinafter, variations of Embodiment 1 are listed. The variations described below can be appropriately combined and applied.

[0198] The engine system 1 of this disclosure includes a computer system as a control unit 11. The computer system is primarily structured with one or more processors and one or more memories as hardware. The processor executes programs stored in the computer system's memory, thereby implementing the functions of the control unit 11 as described in this disclosure. The programs can be pre-stored in the computer system's memory, provided via telecommunication lines, or provided via non-temporary storage media such as memory cards, optical discs, or hard disk drives that can be read by the computer system. Furthermore, some or all of the functional units included in the control unit 11 can also be constructed using electronic circuits.

[0199] Furthermore, integrating at least a portion of the functions of engine system 1 into a single enclosure is not a necessary structure for engine system 1, and the components of engine system 1 can also be distributed across multiple enclosures. For example, control unit 11 can be separated into control unit for exhaust gas recirculation system 4 and control unit for aftertreatment system 5. Conversely, in embodiment 1, functions distributed across multiple devices can also be integrated into a single enclosure.

[0200] The engine body 2 is not limited to a diesel engine using light oil as fuel; for example, it can be a gasoline engine using gasoline as fuel, or a hydrogen fuel cell engine using hydrogen as fuel. Furthermore, the engine system 1 can also be a so-called dual-fuel engine (DF engine), capable of handling either a premixed combustion method where gaseous fuel is mixed with air and then flows into the combustion chamber, or a diffusion combustion method where liquid fuel is injected into the combustion chamber and burned. Here, hydrogen is used as an example of gaseous fuel, and fossil fuels (light oil or gasoline, etc.) are used as an example of liquid fuel. More specifically, by using light oil as liquid fuel, the engine system 1 can handle either a gaseous mode using hydrogen as fuel or a diesel mode using light oil as fuel. In the gaseous mode, a small amount of liquid fuel (light oil, etc.) can also be used as ignition fuel.

[0201] Furthermore, at least a portion of the engine system 1 is not limited to being mounted on the fuselage of the mobile body, but may also be installed separately from the fuselage of the mobile body. As an example, if the control unit 11 is implemented by a server device installed separately from the fuselage of the mobile body, the engine system 1 can be controlled by the control unit 11 through communication between the server device and the mobile body (communication device). At least a portion of the functions of the control unit 11 may also be implemented via the cloud (cloud computing) or the like.

[0202] Furthermore, the mobile body equipped with engine system 1 is not limited to tractors, but can be used in other mobile bodies such as work vehicles, ships, or aircraft. Engine system 1 can also be used in other types of mobile bodies.

[0203] Furthermore, the engine system 1 is not limited to an inline multi-cylinder engine in which multiple cylinders 211 are arranged in a straight line. For example, it may also be a V-type engine or a horizontally opposed engine in which multiple cylinders 211 are arranged in a V-shape with the rotation axis Ax1 of the crankshaft 23 as the vertex.

[0204] Alternatively, engine system 1 can be a single-cylinder engine with only one cylinder 211. Furthermore, engine system 1 is not limited to an engine with a turbocharger; it can also be a naturally aspirated engine without a turbocharger 6.

[0205] (Implementation Method 2)

[0206] like Figure 19 and Figure 20 As shown, in the engine system 1A according to this embodiment, the structure of the aftertreatment system 5 is different from that in embodiment 1. Hereinafter, for structures that are the same as those in embodiment 1, common reference numerals will be used and descriptions will be omitted as appropriate.

[0207] In this embodiment, the aftertreatment system 5 includes a housing 581 that houses the SCR device 51 and the exhaust gas purification device 53. The SCR device 51 and the exhaust gas purification device 53 are connected via a path formed by a portion of the internal space of the housing 581. The housing 581 is, for example, a flat cuboid in the vertical direction D2, and internally houses the first SCR device 51, the first ASC device 54, the exhaust gas purification device 53 (oxidation catalyst 531 and particulate filter 532), the second SCR device 52, and the second ASC device 55. That is, the first SCR housing 501 and the second SCR housing 502 are not separate, but rather the components of the aftertreatment system 5 are housed within a single housing 581.

[0208] In this embodiment, as an example, the housing 581 is disposed above the engine body 2. Here, the housing 581 is supported on the engine body 2 by a support bracket 582. According to this structure, compared with the case where the first SCR housing 501 and the second SCR housing 502 are separately disposed, the support structure (support bracket 582) of the housing 581 can be simplified. Furthermore, it is not necessary to ensure the gap between the first SCR housing 501 and the second SCR housing 502, thus miniaturization can be easily achieved.

[0209] Here, appropriate partitions are formed within the internal space of the housing 581, thereby creating a path (exhaust path 28) for exhaust gas to pass through within the housing 581. Specifically, a path is formed within the internal space of the housing 581 so that exhaust gas passes sequentially through the first SCR device 51, the first ASC device 54, the oxidation catalyst 531, the particulate filter 532, the second SCR device 52, and the second ASC device 55. Furthermore, the exhaust gas inlet in the housing 581 is connected to the booster compressor 6 via the connection path 71.

[0210] In summary, by utilizing the interior of the housing 581 as the exhaust path (exhaust path 28), the piping serving as the exhaust path 28 can be omitted, and structural simplification and miniaturization can be easily achieved. Furthermore, multiple components of the aftertreatment system 5, including the SCR device 51 and the exhaust gas purification device 53, can be held together using an integral housing 581, thus ensuring the rigidity of the aftertreatment system 5 becomes easier.

[0211] Additionally, the exhaust path (connection path 71) leading to the inlet of the SCR device 51 can also be formed within the internal space of the housing 581. In this case, the flexibility in configuring the SCR device 51 within the housing 581 is increased. For example, the configuration of the SCR device 51 or the configuration of the downstream path 73 can be changed according to the mounting requirements of the first reducing agent supply device 56 and the second reducing agent supply device 57, or auxiliary components such as sensors. For example, the first SCR device 51 or the second SCR device 52, whose temperature needs to be maintained, can also be positioned away from the fan.

[0212] Additionally, the housing 581 has a heat-conducting structure that transfers heat from the exhaust gas purification device 53 to the SCR device 51. Figure 20 In the diagram, dashed arrows indicate the movement of heat (thermal conduction). That is, in this embodiment, the housing 581 is made of metal, and the housing 581 itself, or its internal space, becomes a heat-conducting structure, transferring heat from the exhaust gas purification device 53 housed within the same housing 581 to the SCR device 51. Furthermore, the housing 581 houses not only the first SCR device 51 but also the second SCR device 52, thus also transferring heat from the exhaust gas purification device 53 to the second SCR device 52.

[0213] Therefore, the heat stored in the particulate filter 532, which has a relatively large heat capacity, can be transferred to the SCR device 51. Thus, for example, immediately after starting the engine body 2, or when the exhaust gas temperature is low under light load, the time required for the SCR device 51 to reach its activation temperature can be shortened. Similarly, the time required for the second SCR device 52 to reach its activation temperature can also be shortened. Furthermore, compared to using an insulated structure for external piping, cost reduction is easier to achieve.

[0214] In this embodiment, the connection path 71 having a first path 711, a second path 712, and a connecting portion 713 is not necessary in the aftertreatment system 5. That is, the aftertreatment system 5 only needs to include an exhaust gas purification device 53, a (first) SCR device 51, and a housing 581. The exhaust gas purification device 53 captures particulate matter in the exhaust gas discharged from the engine body 2. The SCR device 51 is located between the exhaust port 202 of the engine body 2 and the exhaust gas purification device 53. The housing 581 houses the SCR device 51 and the exhaust gas purification device 53. The SCR device 51 and the exhaust gas purification device 53 are connected through a path formed by a portion of the internal space of the housing 581.

[0215] The structure of Embodiment 2 (including variations) can be appropriately combined with the various structures (including variations) described in Embodiment 1.

[0216] [Notes on the Invention]

[0217] Hereinafter, a summary of the invention extracted from the above embodiments will be noted. Furthermore, the structures and processing functions described in the following notes can be selectively combined arbitrarily.

[0218] <Postscript 1>

[0219] A post-processing system, wherein:

[0220] The connection path connects the exhaust port where exhaust gases are discharged from the engine block to the SCR device.

[0221] The aforementioned connection path has a first path and a second path having lengths in mutually intersecting directions, and a connecting portion connecting the first path and the second path.

[0222] <Appendix 2>

[0223] According to the post-processing system described in Appendix 1, in which,

[0224] The second path described above has a straight section located between the connecting part and the SCR device, which allows the exhaust gas to pass through.

[0225] <Appendix 3>

[0226] According to the post-processing system described in Appendix 1 or 2, it also includes:

[0227] The reducing agent supply device supplies reducing agent into the interior of the aforementioned connection part.

[0228] <Appendix 4>

[0229] According to the post-processing system described in Appendix 3, in which,

[0230] The reducing agent supply device sprays the reducing agent downstream of the flow direction of the exhaust gas.

[0231] <Appendix 5>

[0232] According to the post-processing system described in Appendix 3, in which,

[0233] The reducing agent supply device sprays the reducing agent upstream of the connection point in the direction of the exhaust gas flow.

[0234] <Appendix 6>

[0235] According to any of the post-processing systems described in Appendix 1 to 5, among which,

[0236] The aforementioned connection path has a stirring section at the aforementioned connection part for stirring the aforementioned waste gas.

[0237] <Appendix 7>

[0238] According to any of the post-processing systems described in Appendix 1 to 6, among which,

[0239] The aforementioned connection path is connected to the SCR device from a direction that intersects with the direction of passage of the aforementioned exhaust gas in the SCR device.

[0240] <Postscript 8>

[0241] According to any of the post-processing systems described in notes 1 to 7, among which,

[0242] The aforementioned connection path will discharge the aforementioned exhaust gas introduced from one side to the aforementioned side.

[0243] <Postscript 9>

[0244] According to any of the post-processing systems described in notes 1 to 8, the post-processing system further includes:

[0245] The housing contains the exhaust gas purification device that captures particulate matter in the exhaust gas and the SCR device.

[0246] The SCR device and the exhaust gas purification device are connected via a path formed by a portion of the internal space of the housing.

[0247] <Postscript 10>

[0248] According to the post-processing system described in Appendix 9, among which,

[0249] The aforementioned housing has a heat-conducting structure that transfers heat from the aforementioned exhaust gas purification device to the aforementioned SCR device.

[0250] <Postscript 11>

[0251] An engine system comprising:

[0252] The post-processing system described in any of notes 1 to 10; and

[0253] The aforementioned engine body.

Claims

1. A post-processing system, characterized in that, have: The connection path connects the exhaust port where exhaust gases are discharged from the engine block to the SCR device. The connection path has a first path and a second path having lengths in mutually intersecting directions, and a connecting portion connecting the first path and the second path.

2. The post-processing system according to claim 1, characterized in that, The second path has a straight section located between the connecting part and the SCR device, which allows the exhaust gas to pass through.

3. The post-processing system according to claim 1 or 2, characterized in that, It also has: A reducing agent supply device supplies a reducing agent into the interior of the connecting part.

4. The post-processing system according to claim 3, characterized in that, The reducing agent supply device sprays the reducing agent downstream of the flow direction of the exhaust gas.

5. The post-processing system according to claim 3, characterized in that, The reducing agent supply device sprays the reducing agent upstream of the connection point in the direction of the exhaust gas flow.

6. The post-processing system according to claim 1 or 2, characterized in that, The connection path has a stirring section at the connecting part for stirring the exhaust gas.

7. The post-processing system according to claim 1 or 2, characterized in that, The connection path is connected to the SCR device from a direction that intersects the direction of passage of the exhaust gas in the SCR device.

8. The post-processing system according to claim 1 or 2, characterized in that, The connection path will discharge the exhaust gas introduced from one side to the other side.

9. The post-processing system according to claim 1 or 2, characterized in that, It also has: The housing contains the exhaust gas purification device that captures particulate matter in the exhaust gas and the SCR device. The SCR device and the exhaust gas purification device are connected via a path formed by a portion of the internal space of the housing.

10. The post-processing system according to claim 9, characterized in that, The housing has a thermally conductive structure that transfers heat from the exhaust gas purification device to the SCR device.

11. An engine system, characterized in that, have: The post-processing system as described in claim 1 or 2; and The engine body.

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