Diesel engine

Abstract

To achieve both a quick warm-up of an SCR catalyst and a reduction in NOx.SOLUTION: An engine system includes: an EGR device for perfusing an exhaust gas into an intake passage; an SCR catalyst provided on an exhaust passage; and a control device having a CPU. Based on an engine rotation speed Ne and a fuel injection amount (generation torque Trq correlated to the fuel injection amount), the CPU of the control device calculates a target EGR rate (base EGR rate) (step S125), and calculates a required NOx reduction amount as a reduction target of a NOx amount in the exhaust gas flown out of the SCR catalyst (step S123). The control device further includes a memory for storing a corrected EGR rate map with the engine rotation speed Ne, the fuel injection amount, and the required NOx reduction amount as parameters. Based on the corrected EGR rate acquired from the corrected EGR rate map, the CPU of the control device corrects the target EGR rate (step S125).SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The disclosure relates to a diesel engine, and more particularly to a diesel engine equipped with an EGR device that recirculates exhaust gas to an intake passage, an SCR catalyst provided in the exhaust passage, and a control device including a processor. [Background technology]

[0002] Conventionally, there has been a technique for appropriately purifying nitrogen oxides (hereinafter also referred to as "NOx") while suppressing the amount of urea water added to the SCR catalyst after the engine and SCR catalyst have warmed up (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-179181 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technology of Patent Document 1 does not take into consideration the reduction of NOx from the start of the engine until the warm-up of the SCR catalyst is completed.

[0005] This disclosure has been made to solve the above-mentioned problems, and its purpose is to provide a diesel engine that can achieve both quick warm-up of the SCR catalyst and reduction of NOx. [Means for solving the problem]

[0006] The diesel engine according to the present disclosure includes an EGR device that recirculates a portion of exhaust gas back into an intake passage, an SCR catalyst provided in the exhaust passage, and a control device including a processor. The processor calculates a target EGR rate based on the engine rotation speed and the fuel injection amount, and calculates a required NOx reduction amount, which is a target for reducing the amount of NOx in the exhaust gas flowing out from the SCR catalyst. The control device further includes a memory unit that stores a corrected EGR rate map using the engine rotation speed, the fuel injection amount, and the required NOx reduction amount as parameters. The processor corrects the target EGR rate based on the corrected EGR rate calculated from the corrected EGR rate map.

[0007] Preferably, the processor determines the required NOx reduction amount by adding a value obtained by multiplying the time integral of the difference between the catalytic activation temperature of the SCR catalyst and the current exhaust gas temperature by a first coefficient, a value obtained by multiplying the time integral of the NOx concentration in the exhaust gas entering the SCR catalyst by a second coefficient, and a value obtained by multiplying the time integral of the catalyst passing gas flow rate passing through the SCR catalyst by a third coefficient.

[0008] More preferably, the first coefficient is determined in advance from the correlation between the time integral of the difference between the catalyst activation temperature and the current exhaust gas temperature and the required NOx reduction amount, the second coefficient is determined in advance from the correlation between the time integral of the NOx concentration and the required NOx reduction amount, and the third coefficient is determined in advance from the correlation between the time integral of the catalyst passing gas flow rate and the required NOx reduction amount. [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide a diesel engine that can achieve both quick warm-up of the SCR catalyst and reduction of NOx. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing a schematic configuration of an engine system equipped with a supercharger according to this embodiment. [Figure 2] 1 is a graph showing the relationship between the EGR rate and the time required for the bed temperature of the SCR catalyst to reach a target temperature. [Figure 3]1 is a graph showing the relationship between the EGR rate and the temperature of the exhaust gas entering the SCR catalyst. [Figure 4] 1 is a graph showing the relationship between the EGR rate and the cumulative amount of NOx emitted from the SCR catalyst until the bed temperature of the SCR catalyst reaches a target temperature. [Figure 5] 4 is a flowchart showing the flow of a process for creating a target EGR rate calculation formula according to this embodiment. [Figure 6] 3 is a flowchart showing the flow of an EGR rate control process executed by the control device of the engine system of this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals. The names and functions of the components are also the same. Therefore, detailed description thereof will not be repeated.

[0012] Fig. 1 is a diagram showing a schematic configuration of an engine system 1 equipped with a turbocharger according to this embodiment. In this embodiment, the engine system 1 will be described as a system including a common rail diesel engine, for example, but may also be a system including other types of engines (for example, a unit injector diesel engine, etc.). Furthermore, the engine system 1 is intended to be used to drive equipment such as industrial systems or general-purpose machines, including compressors or hydraulic pumps, but is not limited thereto, and may also be used to drive other machines, such as vehicles.

[0013] The engine system 1 includes an engine body 10, an air cleaner 20, an intercooler 26, an intake manifold 28, a turbocharger 30, an exhaust manifold 50, an exhaust treatment device 55, an exhaust gas recirculation device (hereinafter referred to as an EGR (Exhaust Gas Recirculation) device) 60, an engine rotation speed sensor 102, an air flow meter 104, a boost pressure sensor 106, an outside air temperature sensor 108, an atmospheric pressure sensor 110, and a control device 200.

[0014] The engine body 10 includes a cylinder 12 and an injector 16. The engine body 10 may be an in-line engine, or an engine with another cylinder layout (for example, a V-type or horizontal type).

[0015] The injector 16 is a fuel injection device provided at the top of the cylinder 12 and connected to a common rail (not shown). Fuel stored in a fuel tank (not shown) is pressurized to a predetermined pressure by a supply pump (not shown) and supplied to the common rail. The fuel supplied to the common rail is injected from the injector 16 at a predetermined timing. The injector 16 supplies a fuel injection amount Qv into the cylinder 12 in response to a control signal from the control device 200.

[0016] The air cleaner 20 removes foreign matter from the air drawn in from outside the engine body 10. To the air cleaner 20, one end of a first intake pipe 22 is connected.

[0017] The other end of the first intake pipe 22 is connected to an intake air inlet of a compressor 32 of the turbocharger 30. One end of the second intake pipe 24 is connected to an intake air outlet of the compressor 32. The compressor 32 supercharges the air flowing through the first intake pipe 22 and supplies it to the second intake pipe 24.

[0018] One end of an intercooler 26 is connected to the other end of the second intake pipe 24. The intercooler 26 is an air-cooled or water-cooled heat exchanger that cools the air flowing through the second intake pipe 24.

[0019] One end of a third intake pipe 27 is connected to the other end of the intercooler 26. An intake manifold 28 is connected to the other end of the third intake pipe 27. The intake manifold 28 is connected to the intake ports of the cylinders 12 of the engine body 10. A diesel throttle 25 is provided midway along the third intake pipe 27, closer to the intercooler 26 than the branch point with the EGR 60 (described later). The diesel throttle 25 adjusts the flow rate of intake air in response to a control signal from the control device 200.

[0020] The exhaust manifold 50 is connected to the exhaust ports of the cylinders 12 of the engine body 10. One end of a first exhaust pipe 52 is connected to the exhaust manifold 50. The other end of the first exhaust pipe 52 is connected to an exhaust inlet of the turbine 36 of the turbocharger 30. Therefore, exhaust gas discharged from the exhaust port of each cylinder is supplied to the turbine 36 via the exhaust manifold 50 and the first exhaust pipe 52.

[0021] One end of a second exhaust pipe 54 is connected to the exhaust outlet of the turbine 36. The other end of the second exhaust pipe 54 is connected to an exhaust treatment device 55, a muffler, etc. The exhaust treatment device 55 includes an oxidation catalyst 56, a PM (Particulate Matter) removal filter 57, and an SCR (Selective Catalytic Reduction) catalyst 58. Therefore, the exhaust gas discharged from the exhaust outlet of the turbine 36 passes through the second exhaust pipe 54, the exhaust treatment device 55, the muffler, etc. and is discharged outside the vehicle.

[0022] The oxidation catalyst 56 oxidizes and purifies CO (carbon monoxide), HC (hydrocarbon), and SOF (soluble organic fraction) contained in the exhaust gas. When burning and removing PM trapped in the PM removal filter 57, the oxidation catalyst 56 also burns (oxidizes) the supplied HC, thereby raising the exhaust gas temperature.

[0023] The SCR catalyst 58 is, for example, a ceramic carrier carrying copper (Cu) ion-exchanged zeolite as a catalyst, and exhibits a high NOx (nitrogen oxide) purification rate by using ammonia (NH3) as a reducing agent. The ammonia used as the reducing agent is produced by hydrolysis and thermal decomposition of urea water supplied to the exhaust passage upstream of the SCR catalyst 58. A urea addition valve 80 and a NOx sensor 107 are provided in the exhaust passage upstream of the SCR catalyst 58. The urea addition valve 80 is controlled by a control device 200 to inject urea water, which is pumped from a urea water tank 81 by a pump 82, into the exhaust passage upstream of the SCR catalyst 58. The NOx sensor 107 detects the NOx concentration in the exhaust passage upstream of the SCR catalyst 58. A signal indicating the NOx concentration detected by the NOx sensor 107 is output to the control device 200. The SCR catalyst 58 is provided with a temperature sensor 109 that detects the internal temperature of the SCR catalyst 58. A signal indicating the temperature detected by the temperature sensor 109 is output to the control device 200. Note that an oxidation catalyst that oxidizes and purifies ammonia discharged (slips) from the SCR catalyst 58 may be provided in the exhaust passage downstream of the SCR catalyst 58.

[0024] The third intake pipe 27 (or intake manifold 28) and the first exhaust pipe 52 (or exhaust manifold 50) are connected by an EGR device 60 without passing through the cylinders 12 of the engine body 10. The EGR device 60 includes an EGR valve 62, an EGR passage 66, and an EGR cooler 63. The EGR passage 66 connects the third intake pipe 27 and the first exhaust pipe 52 (or exhaust manifold 50). The EGR valve 62 and the EGR cooler 63 are provided midway through the EGR passage 66. The EGR cooler 63 is an air-cooled or water-cooled heat exchanger that cools the EGR gas that flows to the intake side via the EGR passage 66.

[0025] The EGR valve 62 is an adjustment valve that adjusts the flow rate of EGR gas flowing through the EGR passage 66 in response to a control signal from the control device 200. The exhaust gas in the exhaust manifold 50 is returned to the intake side as EGR gas via the EGR device 60, thereby lowering the combustion temperature in the cylinder 12 and reducing the amount of NOx produced.

[0026] The turbocharger 30 includes a compressor 32, a turbine 36, a variable nozzle mechanism 40, and an actuator 44. A compressor wheel 34 is housed in the housing of the compressor 32, and a turbine wheel 38 is housed in the housing of the turbine 36. The compressor wheel 34 and the turbine wheel 38 are connected by a connecting shaft 42 and rotate integrally. Therefore, the compressor wheel 34 is rotationally driven by the energy of the exhaust gas supplied to the turbine wheel 38.

[0027] Variable nozzle mechanism 40 is arranged at the exhaust inlet portion around the rotation axis of turbine wheel 38, and includes a plurality of vanes (see FIG. 2) that guide exhaust gas supplied from first exhaust pipe 52 to turbine wheel 38, and a link mechanism that changes the gap between adjacent vanes by rotating each of the plurality of vanes (the size of this gap will be referred to as the "VN (vane nozzle) opening" in the following description). Actuator 44 changes the VN opening of variable nozzle mechanism 40 by operating the link mechanism in response to an operation command from control device 200.

[0028] By changing the VN opening of the variable nozzle mechanism 40, the flow path of the exhaust gas at the exhaust gas inlet to the turbine wheel 38 is narrowed or widened, thereby changing the flow velocity of the exhaust gas blown onto the turbine wheel 38.

[0029] The operation of the engine system 1 is controlled by a control device 200. The control device 200 includes a CPU (Central Processing Unit) that performs various processes, memories including a ROM (Read Only Memory) that stores programs and data and a RAM (Random Access Memory) that stores CPU processing results, and input / output ports (none of which are shown) for exchanging information with the outside. The input port is connected to the sensors described above (for example, the engine speed sensor 102, the air flow meter 104, the boost pressure sensor 106, the outside air temperature sensor 108, and the atmospheric pressure sensor 110). The output port is connected to devices to be controlled (for example, the injector 16, the actuator 44, and the EGR valve 62).

[0030] The control device 200 controls various devices based on signals from the sensors and devices, as well as maps and programs stored in memory, so that the engine system 1 operates in a desired state. Note that the various controls are not limited to software processing, but can also be processed by dedicated hardware (electronic circuits). The control device 200 also has a built-in timer circuit (not shown) for measuring time.

[0031] The engine rotation speed sensor 102 detects the rotation speed of the crankshaft, which is the output shaft of the engine body 10, as the engine rotation speed Ne. The engine rotation speed sensor 102 transmits a signal indicating the detected engine rotation speed Ne to the control device 200.

[0032] The air flow meter 104 detects the flow rate (intake air amount) Qin of fresh air introduced into the first intake pipe 22. The air flow meter 104 transmits to the control device 200 a signal indicating the detected intake air amount Qin.

[0033] The supercharging pressure sensor 106 detects the pressure inside the intake manifold 28 as the supercharging pressure. The supercharging pressure sensor 106 transmits a signal indicating the detected supercharging pressure to the control device 200.

[0034] The outside air temperature sensor 108 detects the temperature of the air outside the vehicle in which the engine system 1 is installed. The outside air temperature sensor 108 transmits to the control device 200 a signal indicating the detected outside air temperature.

[0035] The atmospheric pressure sensor 110 detects the pressure of the air outside the vehicle in which the engine system 1 is mounted, that is, the atmospheric pressure. The atmospheric pressure sensor 110 transmits a signal indicating the detected atmospheric pressure to the control device 200.

[0036] Conventionally, there has been a technology that appropriately purifies NOx after the engine body 10 and the SCR catalyst 58 have been warmed up, while suppressing the amount of urea water added to the SCR catalyst 58. However, this technology does not take into consideration the reduction of NOx from the time the engine is started until the warm-up of the SCR catalyst 58 is complete.

[0037] Therefore, the CPU of the control device 200 calculates a target EGR rate based on the engine rotation speed and the fuel injection amount, and when the SCR catalyst 58 is below a predetermined temperature, corrects the target EGR rate and controls the EGR device 60 so that the EGR rate becomes the target EGR rate. This makes it possible to achieve both a quick warm-up of the SCR catalyst 58 and a reduction in NOx.

[0038] FIG. 2 is a graph showing the relationship between the EGR rate and the time it takes for the bed temperature of the SCR catalyst 58 to reach the target temperature. The EGR rate is the ratio of exhaust gas returned to the intake passage (third intake pipe 27) by the EGR device 60 to the intake air. Referring to FIG. 2, this graph is a graph for steady operation under a light load. When the EGR rate is small, the exhaust gas temperature is low, so it takes a longer time to reach the target temperature. When the EGR rate is large, the exhaust gas flow rate is small, so it takes a longer time to reach the target temperature. If the EGR rate is in the medium range, the time it takes for the bed temperature of the SCR catalyst 58 to reach the target temperature is shorter, but the smaller and larger the EGR rate is compared to the medium range, the longer it takes for the bed temperature of the SCR catalyst 58 to reach the target temperature. Note that during warm-up, the EGR rate is usually set to the value u in the graph.

[0039] FIG. 3 is a graph showing the relationship between the EGR rate and the temperature of the exhaust gas entering the SCR catalyst 58. Referring to FIG. 3, this graph is for steady operation under a light load. The higher the EGR rate, the higher the temperature of the exhaust gas entering the SCR catalyst 58. During warm-up, the EGR rate is usually set to the value u in the graph.

[0040] FIG. 4 is a graph showing the relationship between the EGR rate and the cumulative amount of NOx emitted from the SCR catalyst 58 until the bed temperature of the SCR catalyst 58 reaches a target temperature. Referring to FIG. 4, this graph takes into account the heat capacity of the SCR catalyst 58 during steady operation under a light load. As shown in region E, when the EGR rate is a certain value, the cumulative amount of NOx emitted from the SCR catalyst 58 until the bed temperature of the SCR catalyst 58 reaches a target temperature reaches a minimum. During warm-up, the EGR rate is normally set to the value u in the graph. The amount of NOx emitted from the SCR catalyst 58 before warm-up can be easily calculated by correcting the detection value of the NOx sensor 107.

[0041] Generally, when reducing the amount of NOx emitted from the engine body 10, the temperature of the exhaust gas entering the SCR catalyst 58 rises, but the flow rate of fresh air decreases, so the time it takes to warm up the SCR catalyst 58 increases. As shown in Figure 4, there are optimal conditions for the amount of NOx emitted from the engine body in order to reduce the NOx emitted from the SCR catalyst 58 during warm-up. The optimal solution for these conditions depends on the bed temperature of the SCR catalyst 58 before warm-up and on the mechanical differences of the engine system 1. For this reason, for generalization, an evaluation function for the required amount of NOx reduction is considered, as shown in the following equation (1). Note that this reduction amount is the amount reduced from the amount of NOx emitted from the SCR catalyst 58.

[0042]

number

[0043] f(t) is a function that shows the change in (catalyst activation temperature - current exhaust temperature) over time t. In other words, the longer the operation at high exhaust temperatures, the smaller the required NOx reduction amount. g(t) is a function that shows the change in NOx concentration in the exhaust gas entering the SCR catalyst 58 over time t. In other words, the smaller the average NOx emissions, the smaller the required NOx reduction amount. h(t) is a function that shows the change in catalyst passing gas flow rate over time t. In other words, the greater the heat transfer, the greater the required NOx reduction amount.

[0044]

number

[0045] The target EGR rate for controlling the EGR device 60 can be calculated using the above formula (2). The base EGR rate is the conventional EGR rate when warming up the SCR catalyst 58 is not taken into consideration. Ne is the rotation speed of the engine body 10. Trq is the generated torque of the engine body 10. MAP(Ne, Trq, required NOx reduction amount) is a function that specifies the correction torque using a map that defines the correction torque corresponding to the combination of the rotation speed Ne, the generated torque Trq, and the required NOx reduction amount.

[0046] 5 is a flowchart showing the flow of the process for creating a target EGR rate calculation formula according to this embodiment. Referring to FIG. 5, this process is executed by a design computer during the design stage of the engine system 1. This computer includes a CPU and a memory. First, the CPU of the design computer identifies coefficient A in equation (1) above (step S111). Coefficient A is identified from the correlation between the time integral, from time t0 to time t, of the difference between the catalytic activation temperature of the SCR catalyst 58 and the current temperature of the exhaust gas entering the SCR catalyst 58, and the amount of the required NOx reduction that this time integral contributes to.

[0047] Next, the CPU of the design computer determines the coefficient B of the above equation (1) (step S112). The coefficient B is determined from the correlation between the average value of the readings of the NOx sensor 107 from time t0 to time t and the amount of the required NOx reduction that this average value contributes to.

[0048] Next, the CPU of the design computer identifies the coefficient C in the above equation (1) (step S113). The coefficient C is identified from the correlation between the time integral value of the gas flow rate passing through the SCR catalyst 58 from time t0 to time t and the amount of the required NOx reduction amount that this time integral value accounts for.

[0049] Next, the CPU of the design computer creates a map of the above formula (2) (step S114). This map is created so that the corrected EGR rate that maximizes the required NOx reduction amount can be specified for each combination of the rotation speed Ne of the engine body 10 and the generated torque Trq of the engine body 10.

[0050] 6 is a flowchart showing the flow of an EGR rate control process executed by the control device 200 of the engine system 1 according to this embodiment. Referring to FIG. 6, this process is called from a higher-level process by the control device 200 at predetermined intervals and executed.

[0051] First, the CPU of the control device 200 determines whether or not it is the control period of the EGR rate of the EGR device 60 (step S121). If it is determined that it is not the control period (NO in step S121), the CPU of the control device 200 returns the process to be executed to the upper process that called this process.

[0052] On the other hand, if it is determined that the control period has arrived (YES in step S121), it is determined whether the temperature of the SCR catalyst 58 detected by the temperature sensor 109 is below a predetermined temperature, which is the temperature at the end of warm-up (step S122). If it is determined that the temperature of the SCR catalyst 58 is below the predetermined temperature (YES in step S122), the CPU of the control device 200 calculates the required NOx reduction amount using the above equation (1) (step S123). Next, the CPU of the control device 200 calculates the corrected EGR rate using the map of equation (2) (step S124).

[0053] Next, the CPU of the control device 200 corrects the base EGR rate with the correction EGR rate using equation (2) to calculate a target EGR rate (step S125). Then, the CPU controls the EGR valve 62 of the EGR device 60 so that the target EGR rate is achieved (step S126). After step S126, the CPU of the control device 200 returns the process to be executed to the upper process that called this process.

[0054] On the other hand, if it is determined that the temperature of the SCR catalyst 58 has reached or exceeded the predetermined temperature (NO in step S122), the CPU of the control device 200 calculates the base EGR rate as the target EGR rate (step S127). After step S127, the CPU of the control device 200 advances the process to be executed to step S126.

[0055] [Variations] (1) In the embodiment described above, the PM removal filter 57 and the SCR catalyst 58 are configured as separate components. However, the present invention is not limited to this, and the PM removal filter 57 and the SCR catalyst 58 may be configured as an integrated unit.

[0056] (2) The above-described embodiment can be considered as a disclosure of a diesel engine such as the engine system 1 or the control device 200, and can be considered as a disclosure of a control method or control program executed by the control device 200.

[0057] [summary] (1) As shown in FIG. 1, the engine system 1 includes an EGR device 60 that recirculates a portion of exhaust gas into an intake passage, an SCR catalyst 58 provided in the exhaust passage, and a control device 200 including a CPU. As shown in FIG. 6, the CPU of the control device 200 calculates a target EGR rate (e.g., the base EGR rate in equation (2)) based on the engine rotation speed Ne and the fuel injection amount (e.g., a generated torque Trq correlated with the fuel injection amount) (e.g., step S125), and calculates a required NOx reduction amount, which is a reduction target for the amount of NOx in the exhaust gas flowing out from the SCR catalyst 58 (e.g., step S123). As shown in FIG. 1, the control device 200 further includes a memory that stores a correction EGR rate map using the engine rotation speed Ne, the fuel injection amount, and the required NOx reduction amount as parameters. As shown in FIG. 6, the CPU of the control device 200 corrects the target EGR rate based on the correction EGR rate calculated from the correction EGR rate map (e.g., step S125).

[0058] This allows the base EGR rate to be corrected so that, during warm-up when the SCR catalyst 58 is below a predetermined temperature, both the rapid warm-up of the SCR catalyst 58 and the reduction of NOx can be achieved. As a result, both the rapid warm-up of the SCR catalyst 58 and the reduction of NOx can be achieved.

[0059] (2) As shown in equation (1), the CPU of the control device 200 may calculate the required NOx reduction amount by adding together a value obtained by multiplying the time integral of the difference between the catalytic activation temperature of the SCR catalyst 58 and the current exhaust gas temperature by a first coefficient (for example, coefficient A), a value obtained by multiplying the time integral of the NOx concentration in the exhaust gas entering the SCR catalyst 58 by a second coefficient (for example, coefficient B), and a value obtained by multiplying the time integral of the catalyst passing gas flow rate passing through the SCR catalyst 58 by a third coefficient (for example, coefficient C). This makes it possible to more appropriately calculate the required NOx reduction amount.

[0060] 5, the first coefficient may be determined in advance from the correlation between the time integral of the difference between the catalyst activation temperature and the current exhaust gas temperature and the required NOx reduction amount (e.g., step S111), the second coefficient may be determined in advance from the correlation between the time integral of the NOx concentration and the required NOx reduction amount (e.g., step S112), and the third coefficient may be determined in advance from the correlation between the time integral of the catalyst passing gas flow rate and the required NOx reduction amount (e.g., step S113). This allows the coefficients A, B, and C in equation (1) to be calculated appropriately.

[0061] (4) As shown in Fig. 5, the corrected EGR rate may be calculated from the parameters of the engine speed and the fuel injection amount (step S114) in order to achieve the required NOx reduction amount. This allows the corrected EGR rate to be calculated appropriately.

[0062] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0063] 1 engine system, 10 engine body, 12 cylinder, 16 injector, 20 air cleaner, 22 first intake pipe, 24 second intake pipe, 25 diesel throttle, 26 intercooler, 27 third intake pipe, 28 intake manifold, 30 turbocharger, 32 compressor, 34 compressor wheel, 36 turbine, 38 turbine wheel, 40 variable nozzle mechanism, 42 connecting shaft, 44 actuator, 50 exhaust manifold, 52 first exhaust pipe, 54 second exhaust pipe, 55 exhaust treatment device, 56 oxidation catalyst, 57 PM removal filter, 58 SCR catalyst, 60 EGR device, 62 EGR valve, 63 EGR cooler, 66 EGR passage, 80 urea addition valve, 81 urea water tank, 82 pump, 102 engine rotation speed sensor, 104 air flow meter, 105 operation unit, 106 Boost pressure sensor, 107 NOx sensor, 108 outside air temperature sensor, 109 temperature sensor, 110 atmospheric pressure sensor, 200 control device.

Claims

1. A diesel engine including an EGR device that recirculates a portion of exhaust gas into an intake passage, an SCR catalyst provided in the exhaust passage, and a control device including a processor, The processor: A target EGR rate is calculated based on the engine rotation speed and the fuel injection amount. calculating a required NOx reduction amount that is a reduction target for the amount of NOx in the exhaust gas flowing out from the SCR catalyst; the control device further includes a storage unit that stores a corrected EGR rate map using the engine rotation speed, the fuel injection amount, and the required NOx reduction amount as parameters, The processor corrects the target EGR rate based on the correction EGR rate determined from the correction EGR rate map.

2. 2. The diesel engine according to claim 1, wherein the processor calculates the required NOx reduction amount by adding a value obtained by multiplying a time integral of a difference between a catalyst activation temperature of the SCR catalyst and a current exhaust gas temperature by a first coefficient, a value obtained by multiplying a time integral of a NOx concentration in exhaust gas entering the SCR catalyst by a second coefficient, and a value obtained by multiplying a time integral of a catalyst passing gas flow rate passing through the SCR catalyst by a third coefficient.

3. the first coefficient is determined in advance from a correlation between a time integral value of a difference between the catalyst activation temperature and the current exhaust gas temperature and the required NOx reduction amount; the second coefficient is determined in advance from a correlation between the time integral value of the NOx concentration and the required NOx reduction amount; 3. The diesel engine according to claim 2, wherein the third coefficient is determined in advance from a correlation between the time integral value of the catalyst passing gas flow rate and the required NOx reduction amount.

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