Exhaust gas recirculation device and engine

Abstract

[Problem] To provide an exhaust gas recirculation device and an engine capable of controlling the flow rate of exhaust recirculation gas so that the concentration of NOx contained in exhaust gas reaches a target value. [Solution] An exhaust gas recirculation device 3 is provided with: an exhaust pipe 26 that is provided in an exhaust system and guides exhaust; an NOx sensor 53 that is provided in the exhaust pipe 26 and measures the NOx concentration inside the exhaust pipe 26; an exhaust recirculation pipe 27 that is connected to the exhaust pipe 26 and guides exhaust recirculation gas to an intake system; a flow rate adjustment means 28 that is provided in the exhaust recirculation pipe 27 and adjusts the flow rate of the exhaust recirculation gas flowing through the exhaust recirculation pipe 27; and a control device 4 that performs control to calculate a deviation between a target value of the NOx concentration and an actual measurement value of the NOx concentration measured by the NOx sensor 53, derive a correction value on the basis of the calculated deviation, learn the derived correction value and store the correction value as a learned value in a storage unit, and, on the basis of the learned value stored in the storage unit and a basic opening degree of the flow rate adjustment means 28, set a final opening degree of the flow rate adjustment means 28.

Description

Exhaust gas recirculation system and engine

[0001] The present invention relates to an exhaust gas recirculation system and an engine equipped with an exhaust gas recirculation system.

[0002] Exhaust gas recirculation (EGR) is a commonly known method for reducing nitrogen oxides (NOx) contained in engine exhaust gas. An EGR device recirculates a portion of the exhaust gas flowing through the engine's exhaust system back into the engine's intake system as exhaust gas recirculation gas (i.e., EGR gas), and mixes the EGR gas with fresh intake air (i.e., intake air). Compared to a case where an EGR device is not provided, an EGR device can lower the combustion temperature in the cylinder and suppress the generation of NOx.

[0003] Generally, the flow rate adjusting means (i.e., EGR valve) that adjusts the flow rate of exhaust recirculation gas is controlled, for example, by feedback control based on the measurement value of an air flow sensor that measures the flow rate of new intake air (i.e., new intake amount), or by feedback control based on the exhaust gas recirculation rate (i.e., EGR rate) estimated from the measurement value of a pressure sensor or temperature sensor provided in each part of the engine's intake system.

[0004] However, for example, in a small two-cylinder engine, the intake pulsation is larger than in an engine with three or more cylinders, which can make it difficult for an airflow sensor to accurately measure the amount of fresh intake air or to accurately estimate the exhaust gas recirculation rate. Among two-cylinder engines, the intake pulsation is relatively large in two-cylinder engines in which the timing difference between the combustion stroke of the first cylinder and the combustion stroke of the second cylinder is 180 degrees in terms of crankshaft angle. Furthermore, even in engines with three or more cylinders, naturally aspirated engines have larger intake pulsations than turbocharged engines, which can make it difficult for an airflow sensor to accurately measure the amount of fresh intake air or to accurately estimate the exhaust gas recirculation rate. Therefore, feedback control based on measurements from the airflow sensor, pressure sensor, and temperature sensor can sometimes make it difficult to control the flow rate of exhaust gas recirculation so that the NOx concentration in the exhaust gas reaches a target value.

[0005] Furthermore, because the flow rate of the exhaust gas recirculation gas varies depending on the pressure difference between the intake pressure and the exhaust pressure, even when the flow rate adjustment means is controlled by open-loop control, it may be difficult to control the flow rate of the exhaust gas recirculation gas so that the concentration of NOx contained in the exhaust gas reaches a target value. That is, the exhaust pressure depends, for example, on the pressure loss in the muffler. The pressure loss in the muffler depends on the shape of the muffler. Furthermore, the intake pressure depends, for example, on the negative pressure of the air cleaner. The negative pressure of the air cleaner depends on the degree of clogging of the air cleaner and individual differences. Therefore, even when the flow rate adjustment means is controlled by open-loop control, it may be difficult to control the flow rate of the exhaust gas recirculation gas so that the concentration of NOx contained in the exhaust gas reaches a target value.

[0006] Patent Document 1 discloses an EGR device that reduces NOx. The EGR device described in Patent Document 1 determines a target NOx concentration according to the engine's operating state and controls the EGR valve so that the NOx concentration measured by a NOx sensor becomes the target NOx concentration only when the change in the engine's fuel injection amount per unit time is maintained within an allowable range. However, because the response speed of NOx sensors is generally slow, it is difficult to perform feedback control of the EGR valve so that the measured NOx concentration becomes the target NOx concentration.

[0007] JP 2014-15871 A

[0008] The present invention has been made in consideration of the above circumstances, and aims to provide an exhaust gas recirculation device and an engine that can control the flow rate of exhaust recirculation gas so that the concentration of NOx contained in the exhaust gas reaches a target value.

[0009] a control device that calculates a deviation between a target value of the NOx concentration and an actual value of the NOx concentration measured by the NOx sensor, derives a correction value based on the calculated deviation, learns the derived correction value, and stores the learned value in a memory unit, and executes control to set a final opening degree of the flow rate adjustment means based on the learned value stored in the memory unit and a basic opening degree of the flow rate adjustment means.

[0010] a control device that calculates a deviation between a target value of the NOx concentration and an actual value of the NOx concentration measured by the NOx sensor, derives a correction value based on the calculated deviation, learns the derived correction value, and stores the learned value in a memory unit; and executes control to set a final opening degree of the flow rate adjustment means based on the learned value stored in the memory unit and a basic opening degree of the flow rate adjustment means.

[0011] According to the present invention, it is possible to provide an exhaust gas recirculation system and an engine that can control the flow rate of exhaust gas recirculation gas so that the concentration of NOx contained in the exhaust gas reaches a target value.

[0012] FIG. 1 is a schematic diagram showing an engine according to the present embodiment; FIG. 2 is a block diagram showing the main configuration of an exhaust gas recirculation device according to the present embodiment; FIG. 3 is a block diagram explaining the control by which the control device of the present embodiment derives a deviation integral; FIG. 4 is a table illustrating a specific example of an additional value map according to the present embodiment; FIG. 5 is a block diagram explaining the control by which the control device of the present embodiment sets the final opening degree of the flow rate adjustment means; FIG. 6 is a block diagram explaining a modified example of the control by which the control device of the present embodiment sets the final opening degree of the flow rate adjustment means; FIG. 7 is a block diagram explaining a first condition under which the calculation processing unit of the present embodiment learns a correction value; FIG. 8 is a block diagram explaining a second condition under which the calculation processing unit of the present embodiment learns a correction value; FIG. 9 is a graph illustrating the timing under which the calculation processing unit of the present embodiment learns a correction value; FIG. 10 is a flowchart explaining a first specific example of control regarding misfire executed by the control device of the present embodiment; and FIG. 11 is a flowchart explaining a second specific example of control regarding misfire executed by the control device of the present embodiment.

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the embodiments described below are preferred specific examples of the present invention, and therefore various technically preferable limitations are applied, but the scope of the present invention is not limited to these aspects unless otherwise specified in the following description to the effect that the present invention is limited. Furthermore, in each drawing, similar components are given the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0014] Fig. 1 is a schematic diagram showing an engine according to this embodiment, and Fig. 2 is a block diagram showing the configuration of a main part of an exhaust gas recirculation system according to this embodiment.

[0015] The engine 2 according to this embodiment is an internal combustion engine and is a small, naturally aspirated engine. The engine 2 shown in FIG. 1 is an in-line two-cylinder engine. However, the number of cylinders is not particularly limited and may be three or more. The displacement of the engine 2 is approximately 500 cc. However, the displacement is not limited to approximately 500 cc. The timing difference between the combustion stroke of the first cylinder 241 and the combustion stroke of the second cylinder 242 is, for example, 180 degrees in crankshaft angle. However, the timing difference between the combustion stroke of the first cylinder 241 and the combustion stroke of the second cylinder 242 is not limited to this and may be 360 ​​degrees in crankshaft angle. Note that the engine 2 according to this embodiment does not include a turbocharger for supercharging.

[0016] As shown in FIG. 1 , the engine 2 includes an intake manifold 22, a cylinder block 24, and an exhaust manifold 25. The intake manifold 22 is connected to the intake pipe 21 and a cylinder head (not shown), and has a first branch pipe 221 and a second branch pipe 222. The cylinder block 24 has a first cylinder 241 and a second cylinder 242. The first cylinder 241 is connected to the first branch pipe 221 via an intake port (not shown) in the cylinder head. The second cylinder 242 is connected to the second branch pipe 222 via an intake port in the cylinder head. The exhaust manifold 25 is connected to the cylinder head and an exhaust pipe 26. Specifically, the exhaust manifold 25 is connected to the first cylinder 241 and the second cylinder 242 via an exhaust port in the cylinder head. Note that the exhaust pipe 26 may be included in an exhaust gas recirculation system 3, which will be described later.

[0017] The engine 2 also includes a rail 23, a first injector 231, and a second injector 232. The rail 23 is formed in a cylindrical shape and distributes high-pressure fuel supplied from a fuel pump (not shown) to multiple paths according to the number of cylinders of the engine 2. In other words, the rail 23 supplies the high-pressure fuel supplied from the fuel pump to the first injector 231 and the second injector 232.

[0018] The first injector 231 is attached to the rail 23 and is provided so as to protrude toward the combustion chamber formed above the first cylinder 241. The first injector 231 opens and closes a needle valve, for example, by a solenoid, based on a signal sent from the control device 4, and injects fuel supplied from the rail 23 through an injection hole (not shown) into the combustion chamber formed above the first cylinder 241. An example of the control device 4 is an electronic control unit (ECU).

[0019] The second injector 232 is attached to the rail 23 and is provided so as to protrude toward the combustion chamber formed above the second cylinder 242. The second injector 232 opens and closes a needle valve, for example, by a solenoid, based on a signal sent from the control device 4, and injects fuel supplied from the rail 23 through an injection hole into the combustion chamber formed above the second cylinder 242.

[0020] The fuel pressure inside the rail 23 is measured by a pressure sensor 55 attached to the rail 23. The pressure sensor 55 measures the fuel pressure inside the rail 23 and outputs a signal related to the fuel pressure to the control device 4.

[0021] 1, fresh intake air (i.e., intake air) passes through the intake pipe 21, passes through an air cleaner 211 provided in the intake pipe 21, and is led to the intake manifold 22. The intake air led to the intake manifold 22 is distributed to a first branch pipe 221 and a second branch pipe 222, and is led to the first cylinder 241 through the first branch pipe 221 and to the second cylinder 242 through the second branch pipe 222.

[0022] Exhaust gas discharged from the first cylinder 241 and the second cylinder 242 passes through an exhaust manifold 25 and is guided to an exhaust pipe 26. The exhaust gas guided to the exhaust pipe 26 passes through a diesel oxidation catalyst (DOC) 261 provided in the exhaust pipe 26. At this time, the diesel oxidation catalyst 261 oxidizes SOF (Soluble Organic Fraction), CO (Carbon Monoxide), and HC (Hydrocarbon) in PM (Particulate Matter) contained in the exhaust gas. As indicated by arrow A2 in FIG. 1 , the exhaust gas that has passed through the diesel oxidation catalyst 261 passes through the exhaust pipe 26 and is discharged to the outside of the engine 2. The diesel oxidation catalyst 261 may be included in an exhaust gas recirculation device 3, which will be described later.

[0023] Furthermore, the engine 2 is equipped with an exhaust gas recirculation device 3. The exhaust gas recirculation device 3 recirculates a portion of the exhaust gas flowing through the exhaust system of the engine 2 to the intake system of the engine 2 as exhaust gas recirculation gas, thereby reducing nitrogen oxides (NOx) contained in the exhaust gas.

[0024] The exhaust gas recirculation system 3 according to this embodiment includes an exhaust gas recirculation pipe 27 and a flow rate adjusting device 28. As shown in Fig. 1, the exhaust gas recirculation pipe 27 is connected to the exhaust pipe 26 and the intake manifold 22, and guides a portion of the exhaust gas flowing through the exhaust pipe 26 to the intake manifold 22 as exhaust gas recirculation gas. The flow rate adjusting device 28 is called, for example, an EGR valve, and is provided in the exhaust gas recirculation pipe 27. The flow rate adjusting device 28 adjusts the flow rate of the exhaust gas recirculation gas flowing through the exhaust gas recirculation pipe 27 based on a signal transmitted from the control device 4.

[0025] 1 and 2, the exhaust gas recirculation device 3 includes the control device 4, a rotation sensor 51, a NOx sensor 53, a temperature sensor 54, and an accelerator opening sensor 56. The cam angle sensor 52, the pressure sensor 55, and the injectors (i.e., the first injector 231 and the second injector 232) shown in FIG. 2 do not necessarily have to be included in the exhaust gas recirculation device 3, but may be included in the engine 2.

[0026] 2, the control device 4 includes an arithmetic processing unit 41, a storage unit 42, and a communication unit 43. The arithmetic processing unit 41 functions as a CPU (Central Processing Unit), and reads out a program 421 stored in the storage unit 42 to execute various calculations and processes.

[0027] The calculation processing unit 41 receives a detection signal relating to the rotation speed ES of the engine 2 output from the rotation sensor 51 via the communication unit 43. The detection signal relating to the rotation speed ES of the engine 2 is an example of a "first detection signal" in the present invention. The rotation sensor 51 is also called a crank angle sensor, and detects the reference position and rotation angle of the crankshaft of the engine 2 as well as the rotation speed ES of the engine 2, and outputs the detection signals relating to the reference position and rotation angle of the crankshaft and the detection signals relating to the rotation speed ES of the engine 2 to the control device 4.

[0028] The arithmetic processing unit 41 receives, via the communication unit 43, a detection signal relating to the reference position and rotation angle of the camshaft of the engine 2 output from the cam angle sensor 52, and performs cylinder discrimination. The cam angle sensor 52 detects the reference position and rotation angle of the camshaft of the engine 2, and outputs a detection signal relating to the reference position and rotation angle of the camshaft of the engine 2 to the control unit 4.

[0029] The calculation processing unit 41 receives, via the communication unit 43, a detection signal relating to the actual measurement value of the NOx concentration output from the NOx sensor 53. As shown in Fig. 1 , the NOx sensor 53 is provided downstream of the diesel oxidation catalyst 261 in the exhaust pipe 26, and measures the NOx concentration inside the exhaust pipe 26. In addition, the NOx sensor 53 outputs a detection signal relating to the actual measurement value of the measured NOx concentration to the control device 4.

[0030] The calculation processing unit 41 receives a detection signal related to the temperature inside the exhaust pipe 26 output from the temperature sensor 54 via the communication unit 43. As shown in Fig. 1 , the temperature sensor 54 is provided downstream of the diesel oxidation catalyst 261 in the exhaust pipe 26, and measures the temperature inside the exhaust pipe 26. In addition, the temperature sensor 54 outputs a detection signal related to the measured temperature inside the exhaust pipe 26 to the control device 4.

[0031] The calculation processing unit 41 receives the signal relating to the fuel pressure output from the pressure sensor 55 via the communication unit 43. The pressure sensor 55 is as described above.

[0032] The calculation processing unit 41 receives a detection signal relating to the accelerator opening output from the accelerator opening sensor 56 via the communication unit 43. The detection signal relating to the accelerator opening is an example of a "second detection signal" in the present invention. The accelerator opening sensor 56 detects the accelerator opening and outputs the detection signal relating to the accelerator opening to the control device 4.

[0033] The calculation processing unit 41 sets a command value FQD of the fuel injection amount by using, for example, a governor map (not shown) stored in the storage unit 42, based on a detection signal related to the rotation speed ES of the engine 2 output from the rotation sensor 51 and a detection signal related to the accelerator opening degree output from the accelerator opening degree sensor 56. The calculation processing unit 41 outputs a signal related to the set command value FQD of the fuel injection amount to the first injector 231 and the second injector 232 via the communication unit 43. The first injector 231 and the second injector 232 inject fuel supplied from the rail 23 into the combustion chamber based on the command value FQD of the fuel injection amount output from the calculation processing unit 41 via the communication unit 43.

[0034] The arithmetic processing unit 41 sets the opening degree of the flow rate adjustment means 28 and outputs a signal related to the opening degree of the flow rate adjustment means 28 to the flow rate adjustment means 28 via the communication unit 43. Details of the control by the arithmetic processing unit 41 for setting the opening degree of the flow rate adjustment means 28 will be described later. The flow rate adjustment means 28 opens and closes a valve based on the signal related to the opening degree output from the arithmetic processing unit 41 via the communication unit 43, and adjusts the flow rate of the exhaust gas recirculation gas flowing through the exhaust gas recirculation pipe 27.

[0035] The memory unit 42 stores (memorizes) a program 421, a NOx concentration target value map 422, an additional value map 423, a basic opening map 424, a low-speed gain map 425, a medium-speed gain map 426, and a high-speed gain map 427. The memory unit 42 also stores result values ​​of calculations and processes performed by the calculation processing unit 41, learned values ​​learned by the calculation processing unit 41, and the like. Examples of the memory unit 42 include a read-only memory (ROM) and a random-access memory (RAM). The memory unit 42 may be an external storage device connected to the control device 4.

[0036] Examples of the program 421 include an arithmetic program used when the arithmetic processing unit 41 executes calculations and processing, a sequence program used when the arithmetic processing unit 41 executes control described below, and a program for integrating and managing a plurality of programs including these programs. Note that the program 421 is not limited to being stored in the storage unit 42, and may be stored in advance in a storage medium readable by the arithmetic processing unit 41 and distributed, or may be downloaded to the control device 4 via a network.

[0037] The NOx concentration target value map 422 is a map of the rotation speed ES (rpm) of the engine 2 and the fuel injection amount command value FQD (mm ３ / st) and the target value of the NOx concentration, and is used when the calculation processing unit 41 sets the target value of the NOx concentration. The additional value map 423 is map data that shows the relationship between the deviation between the target value of the NOx concentration and the actual value of the NOx concentration measured by the NOx sensor, and an additional value for the deviation integral, which will be described later, and is used when the calculation processing unit 41 sets the additional value for the deviation integral. The "deviation integral" in this embodiment is an example of the "learned value" in the present invention. Furthermore, the "additional value" in this embodiment is an example of the "correction value" in the present invention.

[0038] The basic opening map 424 is map data showing the relationship between the rotation speed ES of the engine 2, the fuel injection amount instruction value FQD, and the basic opening (%) of the flow rate adjustment means 28, and is used when the calculation processing unit 41 sets the basic opening of the flow rate adjustment means 28.

[0039] The low-speed gain map 425, the medium-speed gain map 426, and the high-speed gain map 427 are map data that indicate the relationship between the rotation speed ES of the engine 2, the fuel injection amount command value FQD, and an integral control term gain, which will be described later, and are used when the calculation processing unit 41 sets the integral control term gain. The "integral control term gain" in this embodiment is an example of the "gain" in the present invention.

[0040] Specifically, the low-speed gain map 425 is used by the processing unit 41 when setting the integral control term gain when the rotation speed ES of the engine 2 is low (e.g., less than 1800 rpm). The medium-speed gain map 426 is used by the processing unit 41 when setting the integral control term gain when the rotation speed ES of the engine 2 is medium (e.g., 1800 rpm or more and less than 3100 rpm). The high-speed gain map 427 is used by the processing unit 41 when setting the integral control term gain when the rotation speed ES of the engine 2 is high (e.g., 3100 rpm or more). However, the low (e.g., less than 1800 rpm), medium (e.g., 1800 rpm or more and less than 3100 rpm), and high (e.g., 3100 rpm or more) rotation speeds ES are merely examples and are not limited thereto.

[0041] The aforementioned NOx concentration target value map 422, additional value map 423, basic opening map 424, gain low speed map 425, gain medium speed map 426, and gain high speed map 427 are not limited to map data showing each relationship, but may also be mathematical formulas or distribution diagrams showing each relationship.

[0042] Next, details of the control executed by the control device 4 of this embodiment will be described with reference to the drawings. FIG. 3 is a block diagram illustrating the control by which the control device of this embodiment derives the deviation integral. FIG. 4 is a table illustrating an example of an additional value map of this embodiment. FIG. 5 is a block diagram illustrating the control by which the control device of this embodiment sets the final opening degree of the flow rate adjustment means. FIG. 6 is a block diagram illustrating a modified example of the control by which the control device of this embodiment sets the final opening degree of the flow rate adjustment means.

[0043] 2 and 3 , the calculation processing unit 41 sets a target value 61 of the NOx concentration using a target NOx concentration map 422 based on the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount. Next, the calculation processing unit 41 receives a detection signal related to an actual measurement value 62 of the NOx concentration from the NOx sensor 53, and calculates a deviation 63 between the target value 61 of the NOx concentration and the actual measurement value 62 of the NOx concentration. Specifically, the calculation processing unit 41 calculates the deviation 63 by subtracting the actual measurement value 62 of the NOx concentration from the target value 61 of the NOx concentration.

[0044] Next, the calculation processing unit 41 derives an additional value 64 for the deviation integral using an additional value map 423 based on the calculated deviation 63. As described above with reference to Figures 1 and 2, the "deviation integral" in this embodiment is an example of a "learned value" in the present invention. Also, the "additional value" in this embodiment is an example of a "correction value" in the present invention.

[0045] As shown in the additional value map 423 of FIG. 4, when the deviation 63 is, for example, "5," the calculation processing unit 41 derives "-1" as the additional value 64 for the deviation integral. As such, when the deviation 63 is a positive value, that is, when the actual NOx concentration value 62 is smaller than the target NOx concentration value 61, the calculation processing unit 41 of the present embodiment sets a negative value as the additional value 64 for the deviation integral and controls the flow rate adjustment unit 28 to close. However, when the deviation 63 is a positive value, the calculation processing unit 41 of the present embodiment does not necessarily set a negative value as the additional value 64 for the deviation integral. As shown in the additional value map 423 of FIG. 4, when the deviation 63 is, for example, "1," the calculation processing unit 41 derives "0" as the additional value 64 for the deviation integral and executes control not to operate the flow rate adjustment unit 28.

[0046] On the other hand, as shown in the additional value map 423 in FIG. 4, when the deviation 63 is, for example, "-5," the calculation processing unit 41 derives "1" as the additional value 64 for the deviation integral. In this way, when the deviation 63 is a negative value, that is, when the measured NOx concentration value 62 is greater than the target NOx concentration value 61, the calculation processing unit 41 in this embodiment sets a positive value as the additional value 64 for the deviation integral and controls the flow rate adjustment unit 28 to open. However, the calculation processing unit 41 in this embodiment does not necessarily set a positive value as the additional value 64 for the deviation integral when the deviation 63 is a negative value. As shown in the additional value map 423 in FIG. 4, when the deviation 63 is, for example, "-1," the calculation processing unit 41 derives "0" as the additional value 64 for the deviation integral and executes control not to operate the flow rate adjustment unit 28.

[0047] 3, the calculation processing unit 41 learns the derived added value 64 and stores it in the storage unit 42 as the deviation integral 65. Specifically, the calculation processing unit 41 derives the added value 64 by the control described above every predetermined time (for example, about 5 seconds), and adds the derived added value 64 every predetermined time to the deviation integral 65 stored in the storage unit 42 every predetermined time, thereby updating the deviation integral 65 stored in the storage unit 42 every predetermined time.

[0048] For example, when the deviation integral 65 currently stored in the storage unit 42 is "0," and the deviation 63 after a predetermined time (e.g., about 5 seconds) is "-10," the calculation processing unit 41 derives "2" as the additional value 64 and updates (i.e., sets) the deviation integral 65 to "2 (=0+2)" by adding "2" to the "0" of the deviation integral 65 stored in the storage unit 42. When the deviation 63 after the next predetermined time (e.g., about 5 seconds) is "-5," the calculation processing unit 41 derives "1" as the additional value 64 and adds "1" to the "2" of the deviation integral 65 stored in the storage unit 42, thereby updating (i.e., setting) the deviation integral 65 to "3 (=2+1)." Furthermore, when the deviation 63 is "1" after the next predetermined time (for example, about 5 seconds), the calculation processing unit 41 derives "0" as the added value 64 and updates the deviation integral 65 to "3 (= 3 + 0)" by adding "0" to the "3" of the deviation integral 65 stored in the memory unit 42 (i.e., setting it to remain at "3").

[0049] 2 and 5, the calculation processing unit 41 sets the basic opening 66 of the flow rate adjustment means 28 using the basic opening map 424 based on the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount. Note that the timing when the calculation processing unit 41 sets the basic opening 66 of the flow rate adjustment means 28 is not limited to this timing, and may be a timing in advance (for example, the timing when the calculation processing unit 41 sets the target value 61 of the NOx concentration (see FIG. 3)).

[0050] The calculation processing unit 41 also derives the integral control term gain 67 using a gain map based on the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount. As described above with reference to Figures 1 and 2, the "integral control term gain" in this embodiment is an example of the "gain" of the present invention. Note that the timing at which the calculation processing unit 41 sets the integral control term gain 67 is not limited to this timing, and may be a timing in advance (for example, the timing at which the calculation processing unit 41 sets the target value 61 of the NOx concentration (see Figure 3)).

[0051] Next, the calculation processing unit 41 calculates a value obtained by multiplying the deviation integral 65 stored in the memory unit 42 by an integral control term gain 67. Next, the calculation processing unit 41 adds the value obtained by multiplying the deviation integral 65 by the integral control term gain 67 to the basic opening 66 of the flow rate adjustment unit 28, thereby setting the final opening (%) 68 of the flow rate adjustment unit 28.

[0052] 6 , the calculation processing unit 41 of this embodiment classifies the deviation integral 65 according to the rotation speed ES of the engine 2 and stores the classification in the storage unit 42. Specifically, the calculation processing unit 41 calculates an average value 69 for a calculation cycle (for example, about 5 seconds) of the rotation speed ES of the engine 2. Next, the calculation processing unit 41 classifies the deviation integral 65 to which the addition value 64 is added according to the average value 69 of the rotation speed ES of the engine 2 and stores the classification in the storage unit 42.

[0053] For example, when the average value 69 of the rotation speed ES of the engine 2 is low (e.g., less than 1,800 rpm), the calculation processing unit 41 adds the addend 64 to the deviation integral 651 for low speed stored in the storage unit 42, thereby updating the deviation integral 651 for low speed stored in the storage unit 42. The calculation processing unit 41 also derives a low-speed integral control term gain 671 using the gain low-speed map 425 based on the rotation speed ES of the engine 2 and the fuel injection amount command value FQD. Next, the calculation processing unit 41 uses the low-speed deviation integral 651 in accordance with the average value 69 of the rotation speed ES of the engine 2 to calculate a value obtained by multiplying the low-speed deviation integral 651 by a low-speed integral control term gain 671. Next, the calculation processing unit 41 sets the final opening 68 of the flow rate adjustment unit 28 by adding the value obtained by multiplying the low-speed deviation integral 651 by the low-speed integral control term gain 671 to the basic opening 66 of the flow rate adjustment unit 28.

[0054] For example, when the average value 69 of the rotation speed ES of the engine 2 is a medium speed (e.g., equal to or greater than 1800 rpm and less than 3100 rpm), the calculation processing unit 41 adds the addend 64 to the deviation integral 652 for medium speed stored in the storage unit 42, thereby updating the deviation integral 652 for medium speed stored in the storage unit 42. Furthermore, the calculation processing unit 41 derives the medium speed integral control term gain 672 using the gain map for medium speed 426 based on the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount. Next, the calculation processing unit 41 uses the deviation integral 652 for medium speed in accordance with the average value 69 of the rotation speed ES of the engine 2 to calculate a value obtained by multiplying the medium speed deviation integral 652 by the medium speed integral control term gain 672. Next, the calculation processing unit 41 sets the final opening 68 of the flow rate adjustment means 28 by adding the value obtained by multiplying the deviation integral 652 for medium speed by the integral control term gain 672 for medium speed to the basic opening 66 of the flow rate adjustment means 28.

[0055] For example, when the average value 69 of the engine speed ES of the engine 2 is high (e.g., 3,100 rpm or higher), the calculation processing unit 41 adds the addend 64 to the high-speed deviation integral 653 stored in the storage unit 42, thereby updating the high-speed deviation integral 653 stored in the storage unit 42. The calculation processing unit 41 also derives a high-speed integral control term gain 673 using the high-speed gain map 427 based on the engine speed ES and the fuel injection amount command value FQD. Next, the calculation processing unit 41 uses the high-speed deviation integral 653 in accordance with the average value 69 of the engine speed ES of the engine 2 to calculate a value obtained by multiplying the high-speed deviation integral 653 by a high-speed integral control term gain 673. Next, the calculation processing unit 41 sets the final opening 68 of the flow rate adjustment unit 28 by adding the value obtained by multiplying the high-speed deviation integral 653 by the high-speed integral control term gain 673 to the basic opening 66 of the flow rate adjustment unit 28.

[0056] Next, conditions under which the calculation processing unit 41 of this embodiment learns the added value 64 and stores it in the storage unit 42 as the deviation integral 65 will be described with reference to the drawings. Fig. 7 is a block diagram illustrating a first condition under which the calculation processing unit of this embodiment learns the correction value. Fig. 8 is a block diagram illustrating a second condition under which the calculation processing unit of this embodiment learns the correction value. Fig. 9 is a graph illustrating an example of the timing under which the calculation processing unit of this embodiment learns the correction value.

[0057] The calculation processing unit 41 of this embodiment learns the additional value 64 and stores it in the storage unit 42 as the deviation integral 65 only when the first fluctuation range of the rotation speed ES of the engine 2 for a predetermined time is maintained within a first predetermined range and the second fluctuation range of the command value FQD of the fuel injection amount for a predetermined time is maintained within a second predetermined range. That is, the calculation processing unit 41 learns the additional value 64 and stores it in the storage unit 42 as the deviation integral 65 only when the operating state of the engine 2 is stable. The first predetermined range is, for example, equal to or greater than 0 rpm and less than 30 rpm. The second predetermined range is, for example, equal to or greater than 0 rpm and less than 30 rpm. ３ / st or more, 2mm ３ However, the first and second predetermined ranges are not limited to the ranges shown as examples.

[0058] The calculation processing unit 41 extracts high-frequency components from the rotation speed ES of the engine 2 at a predetermined time, and determines whether or not the operating state of the engine 2 is stable based on a first fluctuation range of the rotation speed ES of the engine 2. For example, as shown in Fig. 7 , the calculation processing unit 41 determines whether or not the operating state of the engine 2 is stable based on the fluctuation range of the high-frequency components extracted by passing the rotation speed ES of the engine 2 through a high-pass filter 71. Note that the calculation processing unit 41 does not necessarily have to use the high-pass filter 71 as long as it can extract predetermined frequency components from the rotation speed ES of the engine 2 at a predetermined time and determine whether or not the operating state of the engine 2 is stable based on the first fluctuation range of the rotation speed ES of the engine 2.

[0059] Furthermore, the calculation processing unit 41 extracts high-frequency components from the command value FQD of the fuel injection amount at a predetermined time and determines whether the operating state of the engine 2 is stable based on a second fluctuation range of the command value FQD of the fuel injection amount. For example, as shown in Fig. 8 , the calculation processing unit 41 determines whether the operating state of the engine 2 is stable based on the fluctuation range of the high-frequency components extracted by passing the command value FQD of the fuel injection amount through a high-pass filter 71. Note that the calculation processing unit 41 does not necessarily need to use the high-pass filter 71 as long as it can extract predetermined frequency components from the command value FQD of the fuel injection amount at a predetermined time and determine whether the operating state of the engine 2 is stable based on the second fluctuation range of the command value FQD of the fuel injection amount.

[0060] The calculation processing unit 41 learns the added value 64 and stores it in the memory unit 42 as the deviation integral 65 only when the first fluctuation range of the engine 2 rotation speed ES at a specified time is maintained within a first specified range and the second fluctuation range of the fuel injection amount instruction value FQD at a specified time is maintained within a second specified range.

[0061] For example, at timing T1 shown in Fig. 9, when the rotation speed ES of the engine 2 is low (e.g., less than 1800 rpm), the first fluctuation range of the rotation speed ES of the engine 2 over a predetermined time period (see "Variation of ES" shown in Fig. 9) is maintained within a first predetermined range, and the second fluctuation range of the command value FQD of the fuel injection amount over a predetermined time period (see "Variation of FQD" shown in Fig. 9) is maintained within a second predetermined range. In this case, the calculation processing unit 41 learns the added value 64 and stores it in the memory unit 42 as the deviation integral 65 (see "Learning ON" shown in Fig. 9).

[0062] At timing T2 shown in Figure 9, when the rotation speed ES of the engine 2 is medium (e.g., equal to or greater than 1800 rpm and less than 3100 rpm), the first fluctuation range of the rotation speed ES of the engine 2 over a predetermined time period (see "Variation of ES" shown in Figure 9) is maintained within a first predetermined range, and the second fluctuation range of the command value FQD of the fuel injection amount over a predetermined time period (see "Variation of FQD" shown in Figure 9) is maintained within a second predetermined range. In this case, the calculation processing unit 41 learns the added value 64 and stores it in the memory unit 42 as the deviation integral 65 (see "Learning ON" shown in Figure 9).

[0063] At timing T3 shown in Fig. 9, when the rotation speed ES of the engine 2 is high (e.g., 3100 rpm or higher), the first fluctuation range of the rotation speed ES of the engine 2 over a predetermined time period (see "Variation of ES" shown in Fig. 9) is maintained within a first predetermined range, and the second fluctuation range of the command value FQD of the fuel injection amount over a predetermined time period (see "Variation of FQD" shown in Fig. 9) is maintained within a second predetermined range. In this case, the calculation processing unit 41 learns the added value 64 and stores it in the memory unit 42 as the deviation integral 65 (see "Learning ON" shown in Fig. 9).

[0064] On the other hand, when the first fluctuation range of the rotation speed ES of the engine 2 over a predetermined time period is not maintained within the first predetermined range, or when the second fluctuation range of the fuel injection amount command value FQD over a predetermined time period is not maintained within the second predetermined range, the calculation processing unit 41 of this embodiment does not learn the additional value 46 and does not store the additional value 64 as a learned value in the storage unit 42. In other words, when the operating state of the engine 2 is not stable, the calculation processing unit 41 does not learn the additional value 46 and does not store the additional value 64 as a learned value in the storage unit 42. In this case, the calculation processing unit 41 sets the final opening degree 68 of the flow rate adjustment means 28 using the deviation integral 65 previously stored in the storage unit 42 (i.e., the deviation integral 65 already stored in the storage unit 42).

[0065] For example, at timing T4 shown in Fig. 9, the first fluctuation range of the rotation speed ES of the engine 2 over a predetermined time period (see "ES Variation" in Fig. 9) is not maintained within the first predetermined range. In this case, the calculation processing unit 41 does not learn the additional value 46 and does not store the additional value 64 as a learned value in the memory unit 42 (see "Learning OFF" in Fig. 9).

[0066] As described above, in the engine 2 according to this embodiment, the control device 4 of the exhaust gas recirculation device 3 does not set the final opening 68 of the flow rate adjustment device based only on the deviation 63 between the target value 61 of the NOx concentration and the actual measured value 62 of the NOx concentration, but derives the additional value 64 based on the deviation 63 between the target value 61 of the NOx concentration and the actual measured value 62 of the NOx concentration, learns the derived additional value 64, and stores it in the memory unit 42 as the deviation integral 65. The control device 4 then sets the final opening 68 of the flow rate adjustment device 28 based on the deviation integral 65 stored in the memory unit 42 and the basic opening 66 of the flow rate adjustment device 28. Specifically, the control device 4 sets the final opening 68 of the flow rate adjustment device 28 by multiplying the integral control term gain 67, which is derived based on the rotational speed ES of the engine 2 and the command value FQD of the fuel injection amount, by the deviation integral 65 stored in the memory unit 42, and adding the result to the basic opening 66 of the flow rate adjustment device 28. As a result, the exhaust gas recirculation device 3 can control the flow rate of the exhaust gas recirculation gas by setting the final opening degree 68 of the flow rate adjustment means 28 so that the actual measured value 62 of NOx concentration becomes the target value 61 of NOx concentration, compared to when the final opening degree 68 of the flow rate adjustment means 28 is set based only on the deviation 63 between the target value 61 of NOx concentration and the actual measured value 62 of NOx concentration.

[0067] Furthermore, the control device 4 updates the deviation integral 65 stored in the memory unit 42 at predetermined time intervals by adding the derived addition value 64 to the deviation integral 65. As a result, even in the case of a NOx sensor 53 with a slow response speed, the control device 4 can use the deviation integral 65 stored in the memory unit 42 to set the final opening degree 68 of the flow rate adjustment means 28 with high precision so that the actual measured value 62 of the NOx concentration becomes the target value 61 of the NOx concentration, thereby controlling the flow rate of the exhaust gas recirculation gas.

[0068] In other words, while a flow sensor typically requires a few milliseconds to perform a measurement, a NOx sensor typically requires several seconds (approximately 100 times longer than a flow sensor). When the control device adjusts the EGR valve opening based on the NOx sensor measurement, it takes several seconds for the resulting NOx concentration to be measured. Therefore, the control device can more accurately control the EGR gas flow rate by gradually changing the EGR valve opening rather than suddenly changing it, since it is easier to grasp the resulting change in NOx concentration. This is one of the reasons why the control device 4 utilizes the deviation integral 65 (see FIG. 3). By utilizing the deviation integral 65, the control device 4 can gradually change the final opening 68 (see FIG. 5) of the flow rate control means 28, thereby more accurately controlling the exhaust gas recirculation gas flow rate.

[0069] The control device 4 also divides the deviation integral 65 according to the rotation speed ES of the engine 2 and stores the divided integrals in the memory unit 42, and uses the divided and stored deviation integrals 65 (in this embodiment, a low-speed deviation integral 651, a medium-speed deviation integral 652, and a high-speed deviation integral 653) in the memory unit 42 according to the rotation speed ES of the engine 2. The control device 4 also derives integral control term gains 67 (in this embodiment, a low-speed integral control term gain 671, a medium-speed integral control term gain 672, and a high-speed integral control term gain 673) divided according to the rotation speed ES of the engine 2, based on the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount. The control device 4 then sets a final opening 68 of the flow rate adjustment device 28 by multiplying the deviation integral 65 stored in the memory unit 42 by the integral control term gain 67 and adding the result to a basic opening 66 of the flow rate adjustment device 28. As a result, the control device 4 can select and use the deviation integral 65 according to the rotational speed ES of the engine 2 in operating regions of the engine 2 where the differential pressure between the intake pressure and the exhaust pressure is different (such as high rotational speed regions and low rotational speed regions) and where the NOx concentration is different (such as high rotational speed regions and low rotational speed regions), and can derive the integral control term gain 67, thereby setting the final opening degree 68 of the flow rate adjustment means 28 with high accuracy so that the actual measured value 62 of the NOx concentration becomes the target value 61 of the NOx concentration according to the operating region of the engine 2, and controlling the flow rate of the exhaust recirculation gas.

[0070] 7 to 9, the control device 4 learns the additional value 64 and stores it in the memory unit 42 as the deviation integral 65 only when the operating state of the engine 2 is stable. As a result, even in the case of a NOx sensor 53 with a slow response speed, the control device 4 learns the additional value 64 only when the operating state of the engine 2 is stable, thereby making it possible to set the final opening degree 68 of the flow rate adjustment means 28 with high accuracy and control the flow rate of the exhaust gas recirculation gas so that the actual measured value 62 of the NOx concentration becomes the target value 61 of the NOx concentration.

[0071] 7 to 9 , when the operating state of the engine 2 is unstable, the control device 4 does not learn the additional value 46 and does not store the additional value 64 as a learned value in the memory unit 42. Then, the control device 4 uses the deviation integral 65 previously stored in the memory unit 42 to set the final opening 68 of the flow rate adjustment device 28 based on the deviation integral 65 and the basic opening 66 of the flow rate adjustment device 28. As a result, even when the operating state of the engine 2 is unstable, the control device 4 can use the deviation integral 65 previously stored in the memory unit 42 to set the final opening 68 of the flow rate adjustment device 28 so that the actual measured value 62 of the NOx concentration becomes the target value 61 of the NOx concentration, thereby controlling the flow rate of the exhaust gas recirculation gas.

[0072] This is another reason why the control device 4 uses the deviation integral 65 (see FIG. 3). That is, by using the deviation integral 65, the control device 4 stores the deviation integral 65 in the memory unit 42 (see FIG. 2). Therefore, when the operating state of the engine 2 is unstable, the control device 4 can use the deviation integral 65 that was previously stored in the memory unit 42. This allows the control device 4 to control the flow rate of the exhaust gas recirculation gas even when the operating state of the engine 2 is unstable.

[0073] Furthermore, the control device 4 learns the added value 64 and stores it in the memory unit 42 as a deviation integral 65 so that the final opening 68 of the flow rate adjustment means 28 becomes larger than the basic opening 66 of the flow rate adjustment means 28 as the operating time of the engine 2 passes. That is, the deviation integral 65 becomes larger as the operating time of the engine 2 passes. In other words, the deviation integral 65 at the time of shipment of the engine 2 from the factory is smaller than the deviation integral 65 after a sufficient operating time of the engine 2 has passed.

[0074] This allows the control device 4 to suppress the flow rate of the exhaust gas recirculation gas and prevent misfires from occurring when the engine 2 is shipped from the factory. The control device 4 then increases the flow rate of the exhaust gas recirculation gas as the operating time of the engine 2 passes, and sets the final opening degree 68 of the flow rate adjustment means 28 so that the actual measured value 62 of the NOx concentration becomes the target value 61 of the NOx concentration, thereby controlling the flow rate of the exhaust gas recirculation gas.

[0075] Next, the control regarding misfire executed by the control device 4 of this embodiment will be described with reference to the drawings. Figure 10 is a flowchart illustrating a first specific example of the control regarding misfire executed by the control device of this embodiment.

[0076] When the control device 4 of this embodiment executes the learning described above with reference to FIGS. 3 to 9 to set the final opening degree 68 of the flow rate adjustment device 28, if the learning is executed incorrectly, it may be difficult to restore normal combustion of abnormal fuel when a misfire occurs. Furthermore, as described above with reference to FIGS. 7 to 9 , the control device 4 of this embodiment learns the added value 64 and stores it in the memory unit 42 as the deviation integral 65 only when the operating state of the engine 2 is stable. Therefore, even if the control device 4 executes the learning correctly, if a misfire occurs, the operating state of the engine 2 may become unstable due to abnormal combustion, and the conditions for the control device 4 to execute the learning may not be met. In this case, it may be difficult to restore normal combustion of abnormal fuel when a misfire occurs. Therefore, as described below, the control device 4 of this embodiment executes control related to misfire.

[0077] That is, when a misfire occurs, the amount of HC (hydrocarbon) contained in the unburned fuel increases and is burned in the diesel oxidation catalyst 261 (see FIG. 1 ). Therefore, when a misfire occurs, the temperature measured by the temperature sensor 54, which is provided downstream of the diesel oxidation catalyst 261 in the exhaust pipe 26, increases compared to when no misfire occurs.

[0078] Therefore, in step S11, the calculation processing unit 41 receives a detection signal relating to the temperature inside the exhaust pipe 26 output from the temperature sensor 54, and determines whether the temperature measured by the temperature sensor 54 is equal to or higher than a predetermined temperature. The predetermined temperature here is, for example, about 500°C. However, the predetermined temperature is not limited to about 500°C.

[0079] If the measured temperature of the temperature sensor 54 is equal to or higher than a predetermined temperature (step S11: YES), in step S12, the calculation processing unit 41 executes at least one of the following controls: a control to multiply the deviation integral 65 by a first predetermined coefficient D1; and a control to multiply the target value 61 of the NOx concentration by a first predetermined coefficient E1.

[0080] The first predetermined coefficient D1 is less than 1.0, for example, approximately 0.8. This reduces the deviation integral 65 compared to when the calculation processing unit 41 does not multiply the deviation integral 65 by the first predetermined coefficient D1. This reduces the final opening degree 68 of the flow rate adjustment unit 28 described above with reference to FIGS. 5 and 6 . In this way, when the temperature measured by the temperature sensor 54 is equal to or higher than the predetermined temperature, the calculation processing unit 41 controls the flow rate adjustment unit 28 to close by multiplying the deviation integral 65 by the first predetermined coefficient D1 as one means. Note that the first predetermined coefficient D1 is not limited to approximately 0.8.

[0081] The first predetermined coefficient E1 is greater than 1.0, for example, approximately 1.2. This increases the target NOx concentration value 61 compared to when the calculation processing unit 41 does not multiply the target NOx concentration value 61 by the first predetermined coefficient E1. Therefore, the deviation 63 described above with reference to FIGS. 3 and 4 increases, and the addition value 64 to the deviation integral decreases. This decreases the deviation integral 65. Therefore, the final opening degree 68 of the flow rate adjustment unit 28 described above with reference to FIGS. 5 and 6 decreases. In this way, when the temperature measured by the temperature sensor 54 is equal to or higher than the predetermined temperature, the calculation processing unit 41 controls the flow rate adjustment unit 28 to close by multiplying the target NOx concentration value 61 by the first predetermined coefficient E1. The first predetermined coefficient E1 is not limited to approximately 1.2.

[0082] Alternatively, in step S12, the calculation processing unit 41 may execute control of subtraction and addition instead of multiplication. In this case, the calculation processing unit 41 executes at least one of control of subtracting a first predetermined coefficient D1 (a positive value) from the deviation integral 65 and control of adding a first predetermined coefficient E1 (a positive value) to the target value 61 of the NOx concentration. Even in this case, the calculation processing unit 41 can control the flow rate adjustment unit 28 to close by executing control of subtracting the first predetermined coefficient D1 from the deviation integral 65 as one means. Furthermore, the calculation processing unit 41 can control the flow rate adjustment unit 28 to close by executing control of adding the first predetermined coefficient E1 to the target value 61 of the NOx concentration as one means.

[0083] On the other hand, if the temperature measured by the temperature sensor 54 is not equal to or higher than the predetermined temperature (step S11: NO), in step S17, the calculation processing unit 41 determines whether the engine 2 has stopped. If the engine 2 has stopped (step S17: YES), the calculation processing unit 41 ends the control related to misfire. On the other hand, if the engine 2 has not stopped (step S17: NO), the calculation processing unit 41 executes the process described above with respect to step S11.

[0084] In step S13 following step S12, the calculation processing unit 41 determines whether a predetermined time has elapsed since the calculation processing unit 41 performed the process described above with respect to step S12. The predetermined time here is, for example, approximately 60 seconds. However, the predetermined time is not limited to approximately 60 seconds. If the predetermined time has elapsed since the calculation processing unit 41 performed the process of step S12 (step S13: YES), in step S14, the calculation processing unit 41 again determines whether the temperature measured by the temperature sensor 54 is equal to or higher than the predetermined temperature. The process of step S14 is the same as the process described above with respect to step S11. On the other hand, if the predetermined time has not elapsed since the calculation processing unit 41 performed the process of step S12 (step S13: NO), the calculation processing unit 41 performs the process of step S13.

[0085] If the measured temperature of the temperature sensor 54 is equal to or higher than the predetermined temperature (step S14: YES), in step S15, the calculation processing unit 41 executes at least one of the following controls: a control to multiply the deviation integral 65 by a second predetermined coefficient D2; and a control to multiply the target value 61 of the NOx concentration by a second predetermined coefficient E2.

[0086] The second predetermined coefficient D2 is less than 1.0, for example, approximately 0.9. As a result, similar to the process described above with respect to step S12, the calculation processing unit 41 controls the flow rate adjusting means 28 in a direction to further close the flow rate adjusting means 28 by multiplying the deviation integral 65 by the second predetermined coefficient D2 as one means. Note that the second predetermined coefficient D2 is not limited to approximately 0.9.

[0087] The second predetermined coefficient E2 is greater than 1.0, for example, approximately 1.1. As a result, similar to the process described above with respect to step S12, the calculation processing unit 41 controls the flow rate adjusting means 28 in a direction to further close the flow rate adjusting means 28 by multiplying the target NOx concentration value 61 by the second predetermined coefficient E2 as one means. Note that the second predetermined coefficient E2 is not limited to approximately 1.1.

[0088] Alternatively, in step S15, the calculation processing unit 41 may execute control of subtraction and addition instead of multiplication. In this case, the calculation processing unit 41 executes at least one of control of subtracting the second predetermined coefficient D2 (a positive value) from the deviation integral 65 and control of adding the second predetermined coefficient E2 (a positive value) to the target value 61 of the NOx concentration. Even in this case, the calculation processing unit 41 can control the flow rate adjustment unit 28 to close by executing control of subtracting the second predetermined coefficient D2 from the deviation integral 65 as one means. Furthermore, the calculation processing unit 41 can control the flow rate adjustment unit 28 to close by executing control of adding the second predetermined coefficient E2 to the target value 61 of the NOx concentration as one means.

[0089] When the calculation processing unit 41 executes control to subtract a predetermined coefficient from the deviation integral 65, the first predetermined coefficient D1 is equal to or greater than the second predetermined coefficient D2. When the calculation processing unit 41 executes control to add a predetermined coefficient to the target value 61 of the NOx concentration, the first predetermined coefficient E1 is equal to or greater than the second predetermined coefficient E2.

[0090] On the other hand, if the temperature measured by the temperature sensor 54 is not equal to or higher than the predetermined temperature (step S14: NO), in step S16, the calculation processing unit 41 cancels the first predetermined coefficient E1 and the second predetermined coefficient E2 related to the NOx concentration target value 61. Step S17 following steps S15 and S16 is as described above with respect to step S17 following step S11.

[0091] As described above, according to this specific example, the control device 4 executes control to reduce the final opening degree 68 of the flow rate adjustment device 28, which adjusts the flow rate of the exhaust gas recirculation gas, when the temperature measured by the temperature sensor 54 reaches or exceeds a predetermined temperature. As a result, the exhaust gas recirculation device 3 according to this embodiment can return abnormal combustion to normal combustion when a misfire occurs, even when the final opening degree 68 of the flow rate adjustment device 28 is controlled by learning using the NOx sensor 53.

[0092] Furthermore, with regard to the predetermined coefficients by which the calculation processing unit 41 multiplies the deviation integral 65, the first predetermined coefficient D1 (approximately 0.8 in this specific example) is equal to or less than the second predetermined coefficient D2 (approximately 0.9 in this specific example). Furthermore, with regard to the predetermined coefficients by which the calculation processing unit 41 multiplies the target value 61 of the NOx concentration, the first predetermined coefficient E1 (approximately 1.2 in this specific example) is equal to or greater than the second predetermined coefficient E2 (approximately 1.1 in this specific example). Alternatively, with regard to the predetermined coefficients by which the calculation processing unit 41 subtracts from the deviation integral 65, the first predetermined coefficient D1 is equal to or greater than the second predetermined coefficient D2. Furthermore, with regard to the predetermined coefficients by which the calculation processing unit 41 adds to the target value 61 of the NOx concentration, the first predetermined coefficient E1 is equal to or greater than the second predetermined coefficient E2. Therefore, when reducing the final opening degree 68 of the flow rate adjustment means 28, the control device 4 reduces the final opening degree 68 of the flow rate adjustment means 28 by a relatively large amount in the initial stage, and then reduces the final opening degree 68 of the flow rate adjustment means 28 by a relatively small amount when the temperature measured by the temperature sensor 54 is still equal to or higher than the predetermined temperature. In this way, the control device 4 can reliably reduce the final opening degree 68 of the flow rate adjustment means 28 while making use of the learned results, and can reliably return abnormal combustion to normal combustion when a misfire occurs.

[0093] 11 is a flowchart illustrating a second example of control regarding misfires executed by the control device of this embodiment. When a misfire occurs, the fluctuations in the rotation speed ES of the engine 2 become larger than when no misfire occurs. When the fluctuations in the rotation speed ES of the engine 2 become larger, the fluctuations in the command value FQD of the fuel injection amount set by the control device 4 also become larger.

[0094] Therefore, in step S21, the calculation processing unit 41 determines whether the fluctuation range of the command value FQD of the fuel injection amount is equal to or greater than a predetermined range. If the fluctuation range of the command value FQD of the fuel injection amount is equal to or greater than the predetermined range (step S21: YES), in step S22, the calculation processing unit 41 executes at least one of the following controls: multiplying the deviation integral 65 by a first predetermined coefficient D1 and multiplying the target value 61 of the NOx concentration by a first predetermined coefficient E1. Alternatively, in step S22, the calculation processing unit 41 executes at least one of the following controls: subtracting the first predetermined coefficient D1 (a positive value) from the deviation integral 65 and adding the first predetermined coefficient E1 (a positive value) to the target value 61 of the NOx concentration. The processing in step S22 is the same as the processing in step S12 described above with reference to FIG. 10 .

[0095] On the other hand, if the fluctuation range of the fuel injection amount command value FQD is not equal to or greater than the predetermined range (step S21: NO), in step S27, the calculation processing unit 41 determines whether or not the engine 2 has stopped. The process of step S27 is the same as the process of step S17 described above with reference to FIG.

[0096] In step S23 following step S22, the calculation processing unit 41 determines whether a predetermined time has elapsed since the calculation processing unit 41 executed the process described above with respect to step S22. The predetermined time here is, for example, approximately one second or more and two seconds or less. However, the predetermined time is not limited to approximately one second or more and two seconds or less. If the predetermined time has elapsed since the calculation processing unit 41 executed the process of step S22 (step S23: YES), in step S24, the calculation processing unit 41 again determines whether the fluctuation range of the fuel injection amount command value FQD is equal to or greater than a predetermined range. The process of step S24 is the same as the process described above with respect to step S21. On the other hand, if the predetermined time has not elapsed since the calculation processing unit 41 executed the process of step S22 (step S23: NO), the calculation processing unit 41 executes the process of step S23.

[0097] If the fluctuation range of the fuel injection amount command value FQD is equal to or greater than the predetermined range (step S24: YES), in step S25, the calculation processing unit 41 executes at least one of the following controls: multiplying the deviation integral 65 by a second predetermined coefficient D2, or multiplying the NOx concentration target value 61 by a second predetermined coefficient E2. Alternatively, in step S25, the calculation processing unit 41 executes at least one of the following controls: subtracting the second predetermined coefficient D2 (a positive value) from the deviation integral 65, or adding the second predetermined coefficient E2 (a positive value) to the NOx concentration target value 61. The processing of step S25 is the same as the processing of step S15 described above with reference to FIG. 10 .

[0098] On the other hand, if the fluctuation range of the fuel injection amount command value FQD is not equal to or greater than the predetermined range (step S24: NO), in step S26, the calculation processing unit 41 cancels the first predetermined coefficient E1 and the second predetermined coefficient E2 related to the NOx concentration target value 61. The process of step S26 is the same as the process of step S16 described above with reference to Fig. 10. Step S25 and step S27 following step S26 are as described above with reference to step S27 following step S21.

[0099] As described above, according to the control of this specific example, the control device 4 executes control to reduce the final opening 68 of the flow rate adjustment device 28, which adjusts the flow rate of exhaust recirculation gas, when the fluctuation range of the fuel injection amount command value FQD exceeds a predetermined range. As a result, the exhaust gas recirculation device 3 according to this embodiment can return abnormal combustion to normal combustion when a misfire occurs, even when the final opening 68 of the flow rate adjustment device 28 is controlled by learning using the NOx sensor 53.

[0100] Furthermore, the process of step S22 is the same as the process of step S12 described above with reference to Fig. 10. Furthermore, the process of step S25 is the same as the process of step S15 described above with reference to Fig. 10. Therefore, the same effects as those described above with reference to Fig. 10 can be obtained.

[0101] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the claims. The configurations of the above embodiments can be partially omitted or arbitrarily combined in a different manner from the above.

[0102] 2: Engine, 3: Exhaust gas recirculation device, 4: Control device, 21: Intake pipe, 22: Intake manifold, 23: Rail, 24: Cylinder block, 25: Exhaust manifold, 26: Exhaust pipe, 27: Exhaust gas recirculation pipe, 28: Flow rate adjusting means, 41: Processing unit, 42: Memory unit, 43: Communication unit, 46: Addition value, 51: Revolution sensor, 52: Cam angle sensor, 53: NOx sensor, 54: Temperature sensor, 55: Pressure sensor, 56: Accelerator opening sensor, 61: Target value of NOx concentration, 62: Actual measured value of NOx concentration, 63: Deviation, 64: Addition value, 65: Deviation integral, 66: Basic opening, 67: Integral control term gain, 68: Final opening, 69: Average value, 71: High-pass filter 211: Air cleaner, 221: First branch pipe, 222: Second branch pipe, 231: First injector, 232: Second injector, 241: First cylinder, 242: Second cylinder, 261: Diesel oxidation catalyst, 421: Program, 422: NOx concentration target value map, 423: Additional value map, 424: Basic opening map, 425: Gain map for low speed, 426: Gain map for medium speed, 427: Gain map for high speed, 651: Deviation integral for low speed, 652: Deviation integral for medium speed, 653: Deviation integral for high speed, 671: Integral control term gain for low speed, 672: Integral control term gain for medium speed, 673: Integral control term gain for high speed

Claims

1. An exhaust gas recirculation device that recirculates a portion of the exhaust flowing through an engine's exhaust system to an intake system of the engine as exhaust recirculation gas, comprising: an exhaust pipe provided in the exhaust system and directing the exhaust; a NOx sensor provided in the exhaust pipe and measuring the NOx concentration inside the exhaust pipe; an exhaust recirculation pipe connected to the exhaust pipe and directing the exhaust recirculation gas to the intake system; a flow rate adjustment means provided in the exhaust recirculation pipe and adjusting the flow rate of the exhaust recirculation gas flowing through the exhaust recirculation pipe; and a control device that calculates a deviation between a target value of the NOx concentration and an actual value of the NOx concentration measured by the NOx sensor, derives a correction value based on the calculated deviation, learns the derived correction value and stores it in a memory unit as a learned value, and executes control to set a final opening of the flow rate adjustment means based on the learned value stored in the memory unit and a basic opening of the flow rate adjustment means.

2. The exhaust gas recirculation device described in claim 1, characterized in that the control device calculates the deviation at predetermined time intervals to derive the correction value, and updates the learning value stored in the memory unit by adding the correction value derived at the predetermined time intervals to the learning value.

3. An exhaust gas recirculation system as described in claim 1, characterized in that the control device sets the final opening by adding the learning value stored in the memory unit to the basic opening.

4. An exhaust gas recirculation device as described in claim 1, further comprising: a rotation sensor which detects the engine speed and outputs a first detection signal related to the engine speed to the control device; and an accelerator opening sensor which detects an accelerator opening and outputs a second detection signal related to the accelerator opening to the control device, wherein the control device sets a command value for the fuel injection amount based on the first detection signal and the second detection signal, derives a gain based on the engine speed and the command value, and sets the final opening by adding a value obtained by multiplying the learning value stored in the memory unit by the gain to the basic opening.

5. An exhaust gas recirculation device as described in claim 1, further comprising a rotation sensor which detects the engine speed and outputs a detection signal related to the engine speed to the control device, wherein the control device divides the learning value according to the engine speed and stores it in the memory unit, uses the learning value divided and stored in the memory unit according to the engine speed, and sets the final opening by adding the learning value to the basic opening.

6. An exhaust gas recirculation device as described in claim 1, further comprising: a rotation sensor which detects the engine speed and outputs a first detection signal related to the engine speed to the control device; and an accelerator opening sensor which detects an accelerator opening and outputs a second detection signal related to the accelerator opening to the control device, wherein the control device sets an instruction value for the fuel injection amount based on the first detection signal and the second detection signal, divides the learning value according to the engine speed and stores it in the memory unit, uses the learning value divided and stored in the memory unit according to the engine speed, derives a gain divided according to the engine speed based on the engine speed and the instruction value, and sets the final opening by adding a value obtained by multiplying the learning value by the gain to the basic opening.

7. An exhaust gas recirculation device as described in claim 1, further comprising: a rotation sensor which detects the engine speed and outputs a first detection signal related to the engine speed to the control device; and an accelerator opening sensor which detects an accelerator opening and outputs a second detection signal related to the accelerator opening to the control device, wherein the control device sets a command value for the fuel injection amount based on the first detection signal and the second detection signal, and learns and stores the correction value in the memory unit as the learned value only when a first fluctuation range of the engine speed at a specified time is maintained within a first specified range and a second fluctuation range of the command value at the specified time is maintained within a second specified range.

8. An exhaust gas recirculation device as described in claim 1, further comprising: a rotation sensor which detects the engine speed and outputs a first detection signal related to the engine speed to the control device; and an accelerator opening sensor which detects an accelerator opening and outputs a second detection signal related to the accelerator opening to the control device, wherein the control device sets a command value for the fuel injection amount based on the first detection signal and the second detection signal, and when a first fluctuation range of the engine speed at a specified time is not maintained within a first specified range, or when a second fluctuation range of the command value at the specified time is not maintained within a second specified range, the control device does not store the correction value as the learning value in the memory unit, but uses the learning value previously stored in the memory unit.

9. An exhaust gas recirculation device as described in claim 1, characterized in that the control device learns the correction value so that the final opening becomes larger than the basic opening as the engine operating time passes, and stores the correction value in the memory unit as the learned value.

10. An engine equipped with an exhaust gas recirculation device that recirculates a portion of the exhaust flowing through an exhaust system to an intake system as exhaust recirculation gas, wherein the exhaust gas recirculation device comprises: an exhaust pipe provided in the exhaust system and directing the exhaust; a NOx sensor provided in the exhaust pipe and measuring the NOx concentration inside the exhaust pipe; an exhaust recirculation pipe connected to the exhaust pipe and directing the exhaust recirculation gas to the intake system; a flow rate adjustment means provided in the exhaust recirculation pipe and adjusting the flow rate of the exhaust recirculation gas flowing through the exhaust recirculation pipe; and a control device that calculates a deviation between a target value of the NOx concentration and an actual value of the NOx concentration measured by the NOx sensor, derives a correction value based on the calculated deviation, learns the derived correction value and stores it in a memory unit as a learned value, and executes control to set a final opening of the flow rate adjustment means based on the learned value stored in the memory unit and a basic opening of the flow rate adjustment means.

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