Exhaust gas recirculation system

Abstract

To provide an exhaust gas recirculation device capable of controlling the flow rate of exhaust recirculation gas so that the concentration of NOx contained in exhaust gas becomes a target value even when a diesel oxidation catalyst is in an inactive state.SOLUTION: The exhaust gas recirculation device 3 includes the exhaust pipe 26, the diesel oxidation catalyst 261, the first temperature sensor 54, the NOx sensor 53, the exhaust circulation pipe 27, the flow rate adjuster 28, the second temperature sensor 57, and the control device 4 that executes control to learn the correction value derived based on the deviation between the target value of the NOx concentration and the actual measurement value of the NOx concentration measured by the NOx sensor and set the final opening degree based on the learned value and the basic opening degree of the flow rate adjuster 28, and executes control to prohibit the learning when the time during which the first temperature and the second temperature are within the predetermined range reaches the predetermined time.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an exhaust gas recirculation system. [Background technology]

[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 when an EGR device is not installed, an EGR device can lower the combustion temperature in the cylinder and suppress the generation of NOx.

[0003] However, when EGR gas is mixed with fresh intake air, the oxygen concentration of the air drawn into the cylinder is lower than when EGR gas is not mixed with fresh intake air. Therefore, if too much EGR gas is mixed with fresh intake air, misfires may occur. When misfires occur, the amount of HC (hydrocarbons) and PM (particulate matter) contained in the exhaust gas increases. In other words, there is a trade-off between reducing NOx and reducing HC and PM.

[0004] Here, Patent Document 1 discloses an EGR device that aims to reduce NOx. The EGR device described in Patent Document 1 determines a target NOx concentration according to the operating state and controls the EGR valve so that the NOx concentration actually measured by the NOx sensor becomes the target NOx concentration only when the amount of change per unit time of the engine fuel injection amount is maintained within an allowable range.

[0005] However, the technology described in Patent Document 1 has a problem in that it cannot detect misfires even when the diesel oxidation catalyst (DOC) is in an inactive state. For example, when a vehicle equipped with an exhaust gas recirculation system goes down a slope or the like and is exposed to strong winds while traveling, the diesel oxidation catalyst cools and becomes inactive. Even if a misfire occurs, the increased HC due to the misfire and the SOF (soluble organic fraction) in the PM are not combusted by the diesel oxidation catalyst. Therefore, even if a misfire occurs when the diesel oxidation catalyst is in an inactive state, the temperature of the exhaust gas downstream of the diesel oxidation catalyst does not increase, resulting in a problem in that the occurrence of a misfire cannot be detected.

[0006] Furthermore, if the engine continues to operate while the diesel oxidation catalyst is in an inactive state and a misfire occurs, HC and SOF will accumulate in the inactive diesel oxidation catalyst. If this happens, the next time the diesel oxidation catalyst becomes active, the HC and SOF accumulated in the diesel oxidation catalyst may be rapidly combusted, resulting in the generation of white smoke.

[0007] Patent Document 2 discloses a DPF system. The DPF system described in Patent Document 2 performs DPF forced regeneration by injecting fuel from an exhaust pipe injector and oxidizing and burning it in a DOC to burn off PM accumulated in the DPF. The DPF system described in Patent Document 2 also includes a temperature sensor and misfire determination means. The temperature sensor is located on the outlet side of the DOC and detects the DOC outlet temperature during DPF forced regeneration. The misfire determination means receives the DOC outlet temperature and determines whether the DOC is maintaining catalytic activity based on the amount of temperature drop per unit time in the DOC outlet temperature. When the misfire determination means determines that the DOC is not maintaining catalytic activity, it interrupts injection from the exhaust pipe injector.

[0008] However, Patent Document 2 does not specifically disclose that when the misfire detection means determines that the DOC is not maintaining catalytic activity, the opening of the EGR valve is controlled to adjust the amount of exhaust gas recirculated from the exhaust manifold to the intake manifold.Even when the DOC is in an inactive state, it is desirable 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. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-15871 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-127299 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made in consideration of the above circumstances, and aims to provide an exhaust gas recirculation device that can control the flow rate of exhaust gas recirculation gas so that the concentration of NOx contained in exhaust gas reaches a target value even when the diesel oxidation catalyst is in an inactive state. [Means for solving the problem]

[0011] A first aspect of the present invention is an exhaust gas recirculation device that recirculates a portion of exhaust gas flowing through an exhaust system of an engine to an intake system of the engine as exhaust recirculation gas, the device comprising: an exhaust pipe provided in the exhaust system and guiding the exhaust; a diesel oxidation catalyst provided in the exhaust pipe; a first temperature sensor provided in the exhaust pipe downstream of the diesel oxidation catalyst and measuring a first temperature inside the exhaust pipe; a NOx sensor provided in the exhaust pipe and measuring a NOx concentration inside the exhaust pipe; an exhaust recirculation pipe connected to the exhaust pipe and guiding the exhaust recirculation gas to the intake system; a control device that learns a correction value derived based on the deviation between the target value of the NOx concentration and the actual value of the NOx concentration measured by the NOx sensor, executes control to set a final opening of the flow rate adjustment device based on the learned value and a basic opening of the flow rate adjustment device, and executes control to prohibit the learning when the time during which the first temperature and the second temperature are within a predetermined range reaches a predetermined time.

[0012] A second aspect of the present invention is an exhaust gas recirculation device that recirculates a portion of exhaust gas flowing through an exhaust system of an engine to an intake system of the engine as exhaust recirculation gas, the device comprising: an exhaust pipe provided in the exhaust system and guiding the exhaust; a diesel oxidation catalyst provided in the exhaust pipe; a NOx sensor provided in the exhaust pipe and measuring a NOx concentration inside the exhaust pipe; an exhaust recirculation pipe connected to the exhaust pipe and guiding the exhaust recirculation gas to the intake system; 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; a rotation sensor that detects the number of revolutions of the engine and outputs a first detection signal related to the number of revolutions; and a control device that sets a command value for the fuel injection amount based on the first detection signal and the second detection signal, learns a correction value derived based on the deviation between the target value of the NOx concentration and the actual value of the NOx concentration measured by the NOx sensor, executes control to set a final opening of the flow rate adjustment means based on the learned value and the basic opening of the flow rate adjustment means, and executes control to prohibit the learning when the time during which the rotation speed and the command value remain within a predetermined range reaches a predetermined time. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide an exhaust gas recirculation device 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 even when the diesel oxidation catalyst becomes inactive. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram illustrating an engine according to an embodiment of the present invention. [Figure 2] 1 is a block diagram showing a configuration of a main part of an exhaust gas recirculation device according to an embodiment of the present invention. [Figure 3] FIG. 3 is a block diagram illustrating control by the control device of the present embodiment to derive a deviation integral. [Figure 4] 4 is a table illustrating an example of an additional value map according to the present embodiment; [Figure 5] FIG. 4 is a block diagram illustrating control by the control device of the present embodiment for setting the final opening degree of the flow rate adjusting means. [Figure 6] FIG. 10 is a block diagram illustrating a modified example of control in which the control device of the present embodiment sets the final opening degree of the flow rate adjusting means. [Figure 7] FIG. 4 is a block diagram illustrating a first condition under which the calculation processing unit of the present embodiment learns a correction value. [Figure 8] FIG. 10 is a block diagram illustrating a second condition under which the calculation processing unit of the present embodiment learns a correction value. [Figure 9] 6 is a graph illustrating timing at which the arithmetic processing unit of the present embodiment learns a correction value. [Figure 10] 4 is a flowchart illustrating a first specific example of control relating to determination of an inactive state of a diesel oxidation catalyst, which is executed by the control device of the present embodiment. [Figure 11] 5 is a flowchart illustrating a second specific example of control relating to determination of the inactive state of the diesel oxidation catalyst, which is executed by the control device of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The embodiments described below are preferred examples of the present invention, and therefore various technically preferable limitations are applied thereto, 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 particularly limited. Furthermore, in each drawing, similar components are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0016] FIG. 1 is a schematic diagram showing an engine according to this embodiment. FIG. 2 is a block diagram showing the configuration of the main parts of the exhaust gas recirculation device according to this embodiment.

[0017] 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.

[0018] 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. The exhaust pipe 26 may be included in an exhaust gas recirculation device 3, which will be described later.

[0019] 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 a plurality of paths according to the number of cylinders of the engine 2. That is, the rail 23 supplies the high-pressure fuel supplied from the fuel pump to the first injector 231 and the second injector 232.

[0020] 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 from 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).

[0021] 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 from an injection hole into the combustion chamber formed above the second cylinder 242.

[0022] 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.

[0023] 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.

[0024] Exhaust gas emitted from the first cylinder 241 and the second cylinder 242 passes through the exhaust manifold 25 and is guided to the 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. 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 the exhaust gas recirculation device 3, which will be described later.

[0025] 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.

[0026] 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 sent from the control device 4.

[0027] 1 and 2, the exhaust gas recirculation device 3 has a control device 4, a rotation sensor 51, a NOx sensor 53, a first temperature sensor 54, an accelerator opening sensor 56, and a second temperature sensor 57. 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, as long as they are included in the engine 2.

[0028] 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.

[0029] 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.

[0030] The calculation 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.

[0031] 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, to the control device 4, a detection signal relating to the actual measurement value of the NOx concentration.

[0032] The calculation processing unit 41 receives a detection signal related to the temperature inside the exhaust pipe 26 output from the first temperature sensor 54 via the communication unit 43. As shown in Fig. 1, the first temperature sensor 54 is provided in the exhaust pipe 26 downstream of the diesel oxidation catalyst 261, and measures the temperature inside the exhaust pipe 26. The first temperature sensor 54 also outputs a detection signal related to the measured temperature inside the exhaust pipe 26 to the control device 4. The temperature measured by the first temperature sensor 54, i.e., the temperature inside the exhaust pipe 26 downstream of the diesel oxidation catalyst 261, is an example of the "first temperature" in the present invention.

[0033] 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.

[0034] 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.

[0035] The calculation processing unit 41 receives a detection signal relating to the temperature of the coolant of the engine 2 output from the second temperature sensor 57 via the communication unit 43. The second temperature sensor 57 measures the temperature of the coolant of the engine 2. The second temperature sensor 57 also outputs a detection signal relating to the measured temperature of the coolant of the engine 2 to the control device 4. The temperature measured by the second temperature sensor 57, i.e., the temperature of the coolant of the engine 2, is an example of the "second temperature" in the present invention.

[0036] 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 memory 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.

[0037] 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 recirculation gas flowing through the exhaust recirculation pipe 27.

[0038] The memory unit 42 stores (memorizes) a program 421, a NOx concentration target value map 422, an additional value map 423, a basic opening degree map 424, a low-speed gain map 425, a medium-speed gain map 426, a high-speed gain map 427, a first counter map 428, and a second counter map 429. The memory unit 42 does not necessarily have to store both the first counter map 428 and the second counter map 429, and may store either the first counter map 428 or the second counter map 429.

[0039] The storage unit 42 stores result values ​​of calculations and processes performed by the calculation processing unit 41, learned values ​​learned by the calculation processing unit 41, etc. Examples of the storage unit 42 include a read-only memory (ROM) and a random access memory (RAM). The storage unit 42 may be an external storage device connected to the control device 4.

[0040] 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 integrally 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.

[0041] 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 showing 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 an additional value for the deviation integral. The "deviation integral" in this embodiment is an example of a "learned value" in the present invention. The "additional value" in this embodiment is an example of a "correction value" in the present invention.

[0042] The basic opening map 424 is map data that shows the relationship between the rotation speed ES of the engine 2, the fuel injection amount indication 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.

[0043] The low speed gain map 425, the medium speed gain map 426, and the high speed gain map 427 are map data showing 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.

[0044] Specifically, the gain low speed map 425 is used by the calculation processing unit 41 to set the integral control term gain when the rotation speed ES of the engine 2 is low (for example, less than 1800 rpm). The gain medium speed map 426 is used by the calculation processing unit 41 to set the integral control term gain when the rotation speed ES of the engine 2 is medium (for example, not less than 1800 rpm and less than 3100 rpm). The gain high speed map 427 is used by the calculation processing unit 41 to set the integral control term gain when the rotation speed ES of the engine 2 is high (for example, not less than 3100 rpm). However, the rotation speeds ES of low speed (for example, less than 1800 rpm), medium speed (for example, not less than 1800 rpm and less than 3100 rpm), and high speed (for example, not less than 3100 rpm) are merely examples and are not limited thereto.

[0045] The first counter map 428 is map data showing the relationship between the temperature measured by the first temperature sensor 54 (i.e., the temperature inside the exhaust pipe 26 downstream of the diesel oxidation catalyst 261), the temperature measured by the second temperature sensor 57 (i.e., the temperature of the coolant of the engine 2), and a counter, and is used when the calculation processing unit 41 increments or decrements a counter related to determining the inactive state of the diesel oxidation catalyst 261. The counters in the first counter map 428 are registered as negative values, zero, and positive values, such as "-1," "0," and "+1." However, the counters registered in the first counter map 428 are not limited to "-1," "0," and "+1," and may be, for example, "-0.5," "0," or "+0.5." Furthermore, the absolute value of a negative value does not necessarily have to be the same as the absolute value of a positive value.

[0046] The second counter map 429 is map data showing the relationship between the rotation speed ES of the engine 2, the fuel injection amount command value FQD, and a counter, and is used when the calculation processing unit 41 increments or decrements a counter related to determining the inactive state of the diesel oxidation catalyst 261. The counters in the second counter map 429 are registered as negative values, zero, and positive values, for example, "-1," "0," and "+1." However, the counters registered in the second counter map 429 are not limited to "-1," "0," and "+1," and may be, for example, "-0.5," "0," "+0.5," etc. Furthermore, the absolute value of a negative value does not necessarily have to be the same as the absolute value of a positive value.

[0047] 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, gain high speed map 427, first counter map 428 and second counter map 429 are not limited to map data showing each relationship, but may also be mathematical formulas or distribution diagrams showing each relationship.

[0048] 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 the additional value map of this embodiment. FIG. 5 is a block diagram illustrating the control performed by the control device of this embodiment to set the final opening degree of the flow rate adjusting means. FIG. 6 is a block diagram illustrating a modified example of control in which the control device of this embodiment sets the final opening degree of the flow rate adjusting means.

[0049] 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.

[0050] Next, the calculation processing unit 41 derives an additional value 64 for the deviation integral using the additional value map 423 based on the calculated deviation 63. As described above with reference to FIGS. 1 and 2, the "deviation integral" in this embodiment is an example of the "learned value" in the present invention. Also, the "additional value" in this embodiment is an example of the "correction value" in the present invention.

[0051] 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. In this way, when the deviation 63 is a positive value, that is, when the measured NOx concentration value 62 is smaller than the target NOx concentration value 61, the calculation processing unit 41 of this 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 this 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.

[0052] On the other hand, 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. 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 of the present embodiment sets a positive value as the additional value 64 for the deviation integral and controls the flow rate adjustment means 28 to open. However, the calculation processing unit 41 of the present 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 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 means 28.

[0053] 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.

[0054] For example, when the deviation integral 65 currently stored in the storage unit 42 is "0," and the deviation 63 after a predetermined time (for example, 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 (for example, 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").

[0055] 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)).

[0056] Furthermore, the calculation processing unit 41 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 FIGS. 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 prior timing (for example, the timing at which the calculation processing unit 41 sets the target value 61 of the NOx concentration (see FIG. 3)).

[0057] 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 means 28, thereby setting the final opening (%) 68 of the flow rate adjustment means 28.

[0058] 6, the calculation processing unit 41 of this embodiment classifies the deviation integral 65 in accordance with the rotation speed ES of the engine 2 and stores the result 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 in accordance with the average value 69 of the rotation speed ES of the engine 2 and stores the result in the storage unit 42.

[0059] For example, when the average value 69 of the rotation speed ES of the engine 2 is low (e.g., less than 1800 rpm), the calculation processing unit 41 adds the addend 64 to the deviation integral for low speed 651 stored in the storage unit 42, thereby updating the deviation integral for low speed 651 stored in the storage unit 42. Furthermore, the calculation processing unit 41 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 command value FQD of the fuel injection amount. 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 the low-speed integral control term gain 671. Next, the calculation processing unit 41 sets a final opening 68 of the flow rate adjustment unit 28 by adding a 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.

[0060] 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. The calculation processing unit 41 also derives an integral control term gain 672 for medium speed using the gain map 426 for medium speed 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 deviation integral 652 for medium speed by an integral control term gain 672 for medium speed. 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 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 unit 28.

[0061] For example, when the average value 69 of the rotation speed ES of the engine 2 is high (e.g., 3100 rpm or higher), the calculation processing unit 41 adds the addend 64 to the deviation integral for high speed 653 stored in the storage unit 42, thereby updating the deviation integral for high speed 653 stored in the storage unit 42. Furthermore, the calculation processing unit 41 derives a high-speed integral control term gain 673 using the gain map for high speed 427 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 for high speed 653 in accordance with the average value 69 of the rotation speed ES of the engine 2 to calculate a value obtained by multiplying the deviation integral for high speed 653 by the integral control term gain for high speed 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 deviation integral for high speed 653 by the integral control term gain for high speed 673 to the basic opening 66 of the flow rate adjustment unit 28.

[0062] Next, the 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 the timing at which the arithmetic processing unit of this embodiment learns the correction value.

[0063] 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 at 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 at 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 / st or less. However, the first and second predetermined ranges are not limited to the ranges given as examples.

[0064] 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.

[0065] 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 or not 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 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 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 or not 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.

[0066] Then, the calculation processing unit 41 learns the added value 64 and stores it in the memory unit 42 as a deviation integral 65 only when the first fluctuation range of the engine speed ES at a predetermined time is maintained within a first predetermined range and the second fluctuation range of the fuel injection amount instruction value FQD at a predetermined time is maintained within a second predetermined range.

[0067] For example, at timing T1 shown in Fig. 9, when the rotation speed ES of the engine 2 is low (for example, less than 1800 rpm), a 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 a 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 additional value 64 and stores it in the memory unit 42 as the deviation integral 65 (see "Learning ON" shown in Fig. 9).

[0068] At timing T2 shown in Fig. 9, when the rotation speed ES of the engine 2 is medium (for example, not less than 1800 rpm and less than 3100 rpm), a 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 a 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 additional value 64 and stores it in the memory unit 42 as the deviation integral 65 (see "Learning ON" shown in Fig. 9).

[0069] At timing T3 shown in Fig. 9, when the rotation speed ES of the engine 2 is high (for example, 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 additional value 64 and stores it in the memory unit 42 as the deviation integral 65 (see "Learning ON" shown in Fig. 9).

[0070] On the other hand, when the first fluctuation range of the rotation speed ES of the engine 2 at a predetermined time is not maintained within the first predetermined range, or when the second fluctuation range of the fuel injection amount command value FQD at a predetermined time 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 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).

[0071] For example, at timing T4 shown in Fig. 9, the first fluctuation range (see "ES Variation" shown in Fig. 9) of the rotation speed ES of the engine 2 over a predetermined time 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" shown in Fig. 9).

[0072] 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. Instead, the control device 4 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 adding a value obtained 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. 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.

[0073] 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 an 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 accuracy 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.

[0074] Generally, a flow sensor takes a few milliseconds to complete a measurement, whereas a NOx sensor takes 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 flow rate of EGR gas by gradually changing the EGR valve opening rather than suddenly changing it, since this allows the control device to grasp the resulting change in NOx concentration. This is one of the reasons why the control device 4 uses the deviation integral 65 (see FIG. 3). By using the deviation integral 65, the control device 4 can gradually change the final opening 68 (see FIG. 5) of the flow rate adjusting means 28, thereby more accurately controlling the flow rate of exhaust gas recirculation gas.

[0075] The control device 4 also divides the deviation integral 65 according to the rotation speed ES of the engine 2 and stores the divided deviation integrals 65 in the memory unit 42, and uses the divided and stored deviation integrals 65 (in this embodiment, a deviation integral 651 for low speed, a deviation integral 652 for medium speed, and a deviation integral 653 for high speed) in the memory unit 42 according to the rotation speed ES of the engine 2. The control device 4 also derives an integral control term gain 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 means 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 means 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.

[0076] 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 the 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 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.

[0077] 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 means 28 based on the deviation integral 65 and the basic opening 66 of the flow rate adjustment means 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 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.

[0078] This is another reason why the control device 4 uses the deviation integral 65 (see FIG. 3). That is, when the control device 4 uses the deviation integral 65, the deviation integral 65 is stored 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 recirculation gas even when the operating state of the engine 2 is unstable.

[0079] Furthermore, the control device 4 learns the additional 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.

[0080] This allows the control device 4 to suppress the flow rate of the exhaust gas recirculation gas and prevent misfires 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 controls 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 the NOx concentration becomes the target value 61 of the NOx concentration.

[0081] Next, the control relating to the determination of the inactive state of the diesel oxidation catalyst 261 executed by the control device 4 of this embodiment will be described with reference to the drawings. FIG. 10 is a flowchart illustrating a first specific example of control relating to the determination of the inactive state of the diesel oxidation catalyst, which is executed by the control device of this embodiment.

[0082] In order to 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 even when the diesel oxidation catalyst 261 becomes inactive, the exhaust gas recirculation device 3 according to this embodiment prohibits the learning described above with reference to FIGS. 3 to 6 when the time during which the measured temperature of the first temperature sensor 54 (i.e., the temperature inside the exhaust pipe 26 downstream of the diesel oxidation catalyst 261) and the measured temperature of the second temperature sensor 57 (i.e., the temperature of the cooling water of the engine 2) are within a predetermined range reaches a predetermined time.

[0083] Specifically, first, in step S1, the calculation processing unit 41 determines whether or not the engine 2 is stopped. If the engine 2 is stopped (step S1: YES), the calculation processing unit 41 ends the control related to the determination of the inactive state of the diesel oxidation catalyst 261.

[0084] On the other hand, if the engine 2 is not stopped (step S1: NO), in step S2, the calculation processing unit 41 determines whether the temperature measured by the second temperature sensor 57 (i.e., the temperature of the coolant of the engine 2) is equal to or higher than the counter start temperature. An example of the counter start temperature is about 50°C. However, the counter start temperature is not limited to 50°C.

[0085] If the temperature measured by the second temperature sensor 57 is not equal to or higher than the counter start temperature (step S2: NO), the calculation processing unit 41 executes the process described above in relation to step S1. On the other hand, if the temperature measured by the second temperature sensor 57 is equal to or higher than the counter start temperature (step S2: YES), in step S3, the calculation processing unit 41 increments or decrements the counter using the first counter map 428 based on the temperature measured by the first temperature sensor 54 (i.e., the temperature inside the exhaust pipe 26 downstream of the diesel oxidation catalyst 261) and the temperature measured by the second temperature sensor 57 (i.e., the temperature of the coolant of the engine 2).

[0086] It should be noted that the counter is "0 (zero)" when the calculation processing unit 41 starts the control of this specific example. In other words, the counter starts from "0." Also, the "counter start temperature" described above in relation to step S2 is the temperature at which the counter starts to increment. In other words, even if the temperature measured by the second temperature sensor 57 is not equal to or higher than the counter start temperature, the counter operates in the background. However, in this case, the counter does not increment.

[0087] The calculation processing unit 41 determines, at predetermined intervals (for example, about 50 milliseconds), in which range of the first counter map 428 the measured temperature of the first temperature sensor 54 and the measured temperature of the second temperature sensor 57 fall, and increments or decrements the counter.

[0088] For example, if the temperatures measured by the first temperature sensor 54 and the second temperature sensor 57 are within a first predetermined range of the first counter map 428, the arithmetic processing unit 41 adds "+1" to the current counter and increments the counter by one. Also, for example, if the temperatures measured by the first temperature sensor 54 and the second temperature sensor 57 are within a second predetermined range of the first counter map 428, the arithmetic processing unit 41 adds "0" to the current counter and maintains the counter. Also, for example, if the temperatures measured by the first temperature sensor 54 and the second temperature sensor 57 are within a third predetermined range of the first counter map 428, the arithmetic processing unit 41 adds "-1" to the current counter and decrements the counter by one. Note that, as described above with reference to FIGS. 1 and 2, the counters registered in the first counter map 428 are not limited to "-1," "0," and "+1."

[0089] In step S4 following step S3, the calculation processing unit 41 determines whether the counter is "100". If the counter is not "100" (step S4: NO), the calculation processing unit 41 executes the process described above with respect to step S3. On the other hand, if the counter is "100" (step S4: YES), in step S5, the calculation processing unit 41 determines that the diesel oxidation catalyst 261 is in an inactive state. In this specific example, the maximum value of the counter is "100" and the minimum value of the counter is "0".

[0090] For example, assume that the time during which the temperatures measured by the first temperature sensor 54 and the second temperature sensor 57 are within the first predetermined range of the first counter map 428 continues for 5 seconds when the calculation processing unit 41 increments or decrements the counter every 50 milliseconds in step S3. In this case, the calculation processing unit 41 continuously executes the process of adding "+1" to the counter every 50 milliseconds for 5 seconds. Therefore, in this case, the counter reaches "100" from "0" in the shortest time possible within 5 seconds.

[0091] Alternatively, for example, when the calculation processing unit 41 increments or decrements the counter every 50 milliseconds in step S3, it is assumed that there is a time during which the temperatures measured by the first temperature sensor 54 and the second temperature sensor 57 are within the first predetermined range and the second predetermined range of the first counter map 428. In this case, the calculation processing unit 41 executes a process of incrementing the counter by "+1" and a process of incrementing the counter by "0" every 50 milliseconds. Therefore, in this case, when the time during which the temperatures measured by the first temperature sensor 54 and the second temperature sensor 57 are within the first predetermined range of the first counter map 428 cumulatively reaches 5 seconds, the counter reaches "100" from "0."

[0092] Alternatively, for example, when the calculation processing unit 41 increments or decrements the counter every 50 milliseconds in step S3, it is assumed that there are times when the temperatures measured by the first temperature sensor 54 and the second temperature sensor 57 are within the first predetermined range, the second predetermined range, and the third predetermined range of the first counter map 428. In this case, the calculation processing unit 41 executes the process of adding "+1", "0", and "-1" to the counter every 50 milliseconds. Therefore, in this case, when the cumulative time during which the temperatures measured by the first temperature sensor 54 and the second temperature sensor 57 are within the first predetermined range of the first counter map 428 reaches a predetermined time, the counter reaches from "0" to "100".

[0093] In this way, when the time during which the temperatures measured by the first temperature sensor 54 and the second temperature sensor 57 are within the first predetermined range of the first counter map 428 continuously or cumulatively reaches a predetermined time, the counter reaches from "0" to "100." Then, as described above, in step S5, the calculation processing unit 41 determines that the diesel oxidation catalyst 261 is in an inactive state. The predetermined time until the counter reaches from "0" to "100" is an example of the "first predetermined time" in the present invention.

[0094] In step S6 following step S5, the calculation processing unit 41 determines whether the temperature measured by the first temperature sensor 54 (i.e., the temperature inside the exhaust pipe 26 downstream of the diesel oxidation catalyst 261) is below a threshold value. The "threshold value" in step S6 is, for example, the lower limit of the fuel ignition temperature of a pre-injection (such as a pilot injection) that is performed before the main injection. An example of the "threshold value" in step S6 is about 140°C. However, the "threshold value" in step S6 is not limited to 140°C.

[0095] If the temperature measured by the first temperature sensor 54 is lower than the threshold value (step S6: YES), in step S7, the calculation processing unit 41 prohibits the learning described above with reference to Figures 3 to 6. In other words, the calculation processing unit 41 prohibits learning the added value 64 and storing it in the memory unit 42 as the deviation integral 65. Then, the calculation processing unit 41 uses the deviation integral 65 previously stored in the memory unit 42 (i.e., the deviation integral 65 already stored in the memory unit 42) to set the final opening 68 of the flow rate adjustment means 28 based on the deviation integral 65 and the basic opening 66 of the flow rate adjustment means 28.

[0096] Also, in step S7, the calculation processing unit 41 executes control to advance the injection timing of the fuel injected from the first injector 231 and the second injector 232. Furthermore, in step S7, the calculation processing unit 41 executes control to stop a pre-injection (such as a pilot injection) that is executed before the main injection.

[0097] On the other hand, if the temperature measured by the first temperature sensor 54 is not less than the threshold value (step S6: NO), in step S8, the calculation processing unit 41 prohibits the learning described above with reference to Figures 3 to 6. In other words, the calculation processing unit 41 prohibits learning the additional value 64 and storing it in the memory unit 42 as the deviation integral 65. Then, the calculation processing unit 41 uses the deviation integral 65 previously stored in the memory unit 42 (i.e., the deviation integral 65 already stored in the memory unit 42) to set the final opening 68 of the flow rate adjustment means 28 based on the deviation integral 65 and the basic opening 66 of the flow rate adjustment means 28.

[0098] In step S8, the calculation processing unit 41 also executes control to advance the injection timing of the fuel injected from the first injector 231 and the second injector 232.

[0099] In step S9 following steps S7 and S8, the calculation processing unit 41 determines whether the counter is "0". If the counter is not "0" (step S9: NO), the calculation processing unit 41 executes the process described above with reference to step S6. On the other hand, if the counter is "0" (step S9: YES), in step S10, the calculation processing unit 41 cancels the determination that the diesel oxidation catalyst 261 is in an inactive state, and resumes the learning described above with reference to Figures 3 to 6. That is, the calculation processing unit 41 resumes learning the additional value 64 and storing it in the memory unit 42 as the deviation integral 65.

[0100] For example, assume that the time during which the temperatures measured by the first temperature sensor 54 and the second temperature sensor 57 are within the third predetermined range of the first counter map 428 continues for five seconds when the calculation processing unit 41 increments or decrements the counter every 50 milliseconds in step S3. In this case, the calculation processing unit 41 continuously executes the process of adding "-1" to the counter every 50 milliseconds for five seconds. Therefore, in this case, the counter reaches "0" from "100" in the shortest time possible, which is five seconds.

[0101] Alternatively, for example, when the calculation processing unit 41 increments or decrements the counter every 50 milliseconds in step S3, it is assumed that there is a time during which the temperatures measured by the first temperature sensor 54 and the second temperature sensor 57 are within the third predetermined range and the second predetermined range of the first counter map 428. In this case, the calculation processing unit 41 executes a process of adding "-1" to the counter and a process of adding "0" to the counter every 50 milliseconds. Therefore, in this case, when the time during which the temperatures measured by the first temperature sensor 54 and the second temperature sensor 57 are within the third predetermined range of the first counter map 428 cumulatively reaches 5 seconds, the counter changes from "100" to "0."

[0102] Alternatively, for example, when the calculation processing unit 41 increments or decrements the counter every 50 milliseconds in step S3, it is assumed that there are times when the temperatures measured by the first temperature sensor 54 and the second temperature sensor 57 are within the third predetermined range, the second predetermined range, and the first predetermined range of the first counter map 428. In this case, the calculation processing unit 41 executes the process of adding "-1", "0", and "+1" to the counter every 50 milliseconds. Therefore, in this case, when the cumulative time during which the temperatures measured by the first temperature sensor 54 and the second temperature sensor 57 are within the third predetermined range of the first counter map 428 reaches a predetermined time, the counter changes from "100" to "0".

[0103] In this way, when the time during which the temperatures measured by the first temperature sensor 54 and the second temperature sensor 57 are within the third predetermined range of the first counter map 428, i.e., the time during which the temperatures measured by the first temperature sensor 54 and the second temperature sensor 57 are outside the first predetermined range of the first counter map 428, continuously or cumulatively reaches a predetermined time, the counter reaches "0" from "100." Then, as described above, in step S9, the calculation processing unit 41 cancels the determination that the diesel oxidation catalyst 261 is in an inactive state and resumes the learning described above with reference to FIGS. 3 to 6. The predetermined time until the counter reaches "0" from "100" is an example of the "second predetermined time" of the present invention. Following step S9, the calculation processing unit 41 executes the process described above with reference to step S3.

[0104] According to this specific example, when the time during which the temperature measured by the first temperature sensor 54 and the temperature measured by the second temperature sensor 57 are within the first predetermined range of the first counter map 428 reaches a predetermined time, the calculation processing unit 41 determines that the diesel oxidation catalyst 261 is in an inactive state and prohibits learning the added value 64 and storing it in the memory unit 42 as the deviation integral 65. Then, the calculation processing unit 41 uses the deviation integral 65 previously stored in the memory unit 42 (i.e., the deviation integral 65 already stored in the memory unit 42) to set the final opening 68 of the flow rate adjustment means 28 based on the deviation integral 65 and the basic opening 66 of the flow rate adjustment means 28. As a result, the exhaust gas recirculation device 3 according to this embodiment can 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, even when the diesel oxidation catalyst 261 is in an inactive state.

[0105] Furthermore, when the calculation processing unit 41 determines that the diesel oxidation catalyst 261 is in an inactive state, it advances the injection timing of the fuel injected from the first injector 231 and the second injector 232. This reduces the amount of HC (hydrocarbons) contained in the exhaust gas, and makes it possible to reduce the amount of HC that accumulates in the inactive diesel oxidation catalyst 261. This makes it possible to prevent the HC that has accumulated in the diesel oxidation catalyst 261 from being rapidly burned and generating white smoke the next time the diesel oxidation catalyst 261 becomes active.

[0106] Furthermore, when the calculation processing unit 41 determines that the diesel oxidation catalyst 261 is in an inactive state, it stops the pre-injection (pilot injection, etc.) if the temperature measured by the first temperature sensor 54 is below a threshold value. Therefore, for example, when the temperature measured by the first temperature sensor 54 is below the threshold value, it is possible to suppress the occurrence of fuel misignition in the pre-injection (pilot injection, etc.). This makes it possible to suppress an increase in HC contained in the exhaust gas and an increase in HC that accumulates in the inactive diesel oxidation catalyst 261. As a result, the next time the diesel oxidation catalyst 261 becomes active, it is possible to suppress the rapid combustion of HC accumulated in the diesel oxidation catalyst 261 and the generation of white smoke.

[0107] FIG. 11 is a flowchart illustrating a second specific example of control relating to the determination of the inactive state of the diesel oxidation catalyst, which is executed by the control device of this embodiment. In addition, in cases where the control processing according to the second specific example is similar to the control processing according to the first specific example described above with reference to FIG. 10, duplicated explanations will be omitted as appropriate, and the following explanation will focus on the differences.

[0108] In order to 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 even when the diesel oxidation catalyst 261 becomes inactive, the exhaust gas recirculation device 3 according to this embodiment prohibits the learning described above with reference to FIGS. 3 to 6 when the time during which the rotation speed ES of the engine 2 output from the rotation sensor 51 and the indicated value FQD of the fuel injection amount set by the calculation processing unit 41 are within a predetermined range reaches a predetermined time.

[0109] More specifically, first, the processes of steps S11 and S12 are the same as the processes of steps S1 and S2, respectively, described above with reference to Fig. 10. In step S13 following step S12, the calculation processing unit 41 increments or decrements the counter using the second counter map 429 based on the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount.

[0110] 10, when the calculation processing unit 41 starts the control of this specific example, the counter is "0 (zero)." In other words, the counter starts from "0." The calculation processing unit 41 determines, at predetermined time intervals (for example, about 50 milliseconds), in which range of the second counter map 429 the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount are within, and increments or decrements the counter.

[0111] For example, when the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount are within a first predetermined range of the second counter map 429, the calculation processing unit 41 adds "+1" to the current counter and increments the counter by one. Also, when the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount are within a second predetermined range of the second counter map 429, the calculation processing unit 41 adds "0" to the current counter and maintains the counter. Also, when the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount are within a third predetermined range of the second counter map 429, the calculation processing unit 41 adds "-1" to the current counter and decrements the counter by one. As described above with reference to FIGS. 1 and 2, the counters registered in the second counter map 429 are not limited to "-1," "0," and "+1."

[0112] The process of step S14 following step S13 is the same as the process of step S4 described above with reference to FIG.

[0113] For example, when the calculation processing unit 41 increments or decrements the counter every 50 milliseconds in step S13, it is assumed that the time during which the rotation speed ES of the engine 2 and the fuel injection amount command value FQD are within the first predetermined range of the second counter map 429 continues for 5 seconds. In this case, the calculation processing unit 41 continuously executes the process of adding "+1" to the counter every 50 milliseconds for 5 seconds. Therefore, in this case, the counter reaches "100" from "0" in the shortest time of 5 seconds.

[0114] Alternatively, for example, when the calculation processing unit 41 increments or decrements the counter every 50 milliseconds in step S13, it is assumed that there is a time during which the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount are within the first predetermined range and the second predetermined range of the second counter map 429. In this case, the calculation processing unit 41 executes a process of incrementing the counter by 1 and a process of incrementing the counter by 0 every 50 milliseconds. Therefore, in this case, when the time during which the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount are within the first predetermined range of the second counter map 429 cumulatively reaches 5 seconds, the counter reaches 100 from 0.

[0115] Alternatively, for example, when the calculation processing unit 41 increments or decrements the counter every 50 milliseconds in step S13, it is assumed that there is a time during which the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount are within the first predetermined range, the second predetermined range, and the third predetermined range of the second counter map 429. In this case, the calculation processing unit 41 executes the process of adding "+1", "0", and "-1" to the counter every 50 milliseconds. Therefore, in this case, when the time during which the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount are within the first predetermined range of the second counter map 429 cumulatively reaches a predetermined time, the counter reaches from "0" to "100".

[0116] In this way, when the time during which the rotation speed ES of the engine 2 and the fuel injection amount command value FQD are within the first predetermined range of the second counter map 429 continuously or cumulatively reaches a predetermined time, the counter reaches from "0" to "100." Then, in step S15, the calculation processing unit 41 determines that the diesel oxidation catalyst 261 is in an inactive state. The predetermined time until the counter reaches from "0" to "100" is an example of the "first predetermined time" in the present invention.

[0117] The processes in steps S16 to S20 are the same as the processes in steps S6 to S10 described above with reference to FIG.

[0118] For example, in step S19 following steps S17 and S18, if the calculation processing unit 41 increments or decrements the counter every 50 milliseconds in step S13, it is assumed that the time during which the rotation speed ES of the engine 2 and the fuel injection amount command value FQD are within the third predetermined range of the second counter map 429 continues for 5 seconds. In this case, the calculation processing unit 41 continuously executes the process of adding "-1" to the counter every 50 milliseconds for 5 seconds. Therefore, in this case, the counter reaches "0" from "100" in the shortest time of 5 seconds.

[0119] Alternatively, for example, when the calculation processing unit 41 increments or decrements the counter every 50 milliseconds in step S13, it is assumed that there is a time during which the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount are within the third predetermined range and the second predetermined range of the second counter map 429. In this case, the calculation processing unit 41 executes a process of incrementing the counter by "-1" and a process of incrementing the counter by "0" every 50 milliseconds. Therefore, in this case, when the time during which the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount are within the third predetermined range of the second counter map 429 cumulatively reaches 5 seconds, the counter changes from "100" to "0."

[0120] Alternatively, for example, when the calculation processing unit 41 increments or decrements the counter every 50 milliseconds in step S13, it is assumed that there is a time during which the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount are within the third predetermined range, the second predetermined range, and the first predetermined range of the second counter map 429. In this case, the calculation processing unit 41 executes the process of adding "-1", "0", and "+1" to the counter every 50 milliseconds. Therefore, in this case, when the time during which the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount are within the third predetermined range of the second counter map 429 cumulatively reaches a predetermined time, the counter changes from "100" to "0".

[0121] In this way, when the time during which the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount are within the third predetermined range of the second counter map 429, i.e., the time during which the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount are outside the first predetermined range of the second counter map 429, continuously or cumulatively reaches a predetermined time, the counter reaches "0" from "100". Then, in step S19, the calculation processing unit 41 cancels the determination that the diesel oxidation catalyst 261 is in an inactive state, and resumes the learning described above with reference to Figures 3 to 6. The predetermined time during which the counter reaches "0" from "100" is an example of the "second predetermined time" in the present invention.

[0122] According to this specific example, when the time during which the rotation speed ES of the engine 2 and the command value FQD of the fuel injection amount are within the first predetermined range of the second counter map 429 reaches a predetermined time, the calculation processing unit 41 determines that the diesel oxidation catalyst 261 is in an inactive state and prohibits learning the added value 64 and storing it in the memory unit 42 as the deviation integral 65. Then, the calculation processing unit 41 uses the deviation integral 65 previously stored in the memory unit 42 (i.e., the deviation integral 65 already stored in the memory unit 42) to set the final opening 68 of the flow rate adjustment means 28 based on the deviation integral 65 and the basic opening 66 of the flow rate adjustment means 28. As a result, the exhaust gas recirculation device 3 according to this embodiment can 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, even when the diesel oxidation catalyst 261 is in an inactive state. Furthermore, the same effects as those described with reference to FIG. 10 can be obtained.

[0123] 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. [Explanation of symbols]

[0124] 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: First temperature sensor, 55: Pressure sensor, 56: Accelerator opening sensor, 57: Second temperature 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, 428: First counter map, 429: Second counter map, 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 exhaust gas flowing through an exhaust system of an engine to an intake system of the engine as exhaust gas recirculation gas, an exhaust pipe provided in the exhaust system and guiding the exhaust; a diesel oxidation catalyst provided in the exhaust pipe; a first temperature sensor that is provided in the exhaust pipe downstream of the diesel oxidation catalyst and that measures a first temperature inside the exhaust pipe; a NOx sensor provided in the exhaust pipe for measuring a NOx concentration inside the exhaust pipe; an exhaust gas recirculation pipe connected to the exhaust pipe and guiding the exhaust gas recirculation gas to the intake system; a flow rate adjusting means provided in the exhaust gas recirculation pipe for adjusting the flow rate of the exhaust gas recirculation gas flowing through the exhaust gas recirculation pipe; a second temperature sensor for measuring a second temperature of the engine coolant; a control device that learns a correction value derived based on a deviation between the target value of the NOx concentration and the actual value of the NOx concentration measured by the NOx sensor, executes control to set a final opening of the flow rate adjustment means based on the learned value and a basic opening of the flow rate adjustment means, and executes control to prohibit the learning when a predetermined time has elapsed during which the first temperature and the second temperature are within a predetermined range; An exhaust gas recirculation device comprising:

2. 2. The exhaust gas recirculation device according to claim 1, wherein the control device further executes control to advance the injection timing of fuel injected from the injector when the time during which the first temperature and the second temperature are in the predetermined range reaches the predetermined time.

3. 2. The exhaust gas recirculation device according to claim 1, wherein the control device further performs control to stop a pre-injection that is performed before a main injection when the time during which the first temperature and the second temperature are in the predetermined range reaches the predetermined time and the first temperature is less than a threshold value.

4. the predetermined time is a first predetermined time, 2. The exhaust gas recirculation device according to claim 1, wherein the control device executes control to prohibit the learning, and then executes control to resume the learning when the time during which the first temperature and the second temperature are outside the predetermined range reaches a second predetermined time.

5. An exhaust gas recirculation device that recirculates a portion of exhaust gas flowing through an exhaust system of an engine to an intake system of the engine as exhaust gas recirculation gas, an exhaust pipe provided in the exhaust system and guiding the exhaust; a diesel oxidation catalyst provided in the exhaust pipe; a NOx sensor provided in the exhaust pipe for measuring a NOx concentration inside the exhaust pipe; an exhaust gas recirculation pipe connected to the exhaust pipe and guiding the exhaust gas recirculation gas to the intake system; a flow rate adjusting means provided in the exhaust gas recirculation pipe for adjusting the flow rate of the exhaust gas recirculation gas flowing through the exhaust gas recirculation pipe; a rotation sensor that detects the number of revolutions of the engine and outputs a first detection signal related to the number of revolutions; an accelerator opening sensor that detects an accelerator opening and outputs a second detection signal related to the accelerator opening; a control device that sets an instruction value of a fuel injection amount based on the first detection signal and the second detection signal, learns a correction value derived based on a deviation between the target value of the NOx concentration and the actual value of the NOx concentration measured by the NOx sensor, executes control to set a final opening of the flow rate adjustment means based on the learned value and a basic opening of the flow rate adjustment means, and executes control to prohibit the learning when a time during which the rotation speed and the instruction value remain within a predetermined range reaches a predetermined time; An exhaust gas recirculation device comprising:

6. 6. The exhaust gas recirculation system according to claim 5, wherein the control device further executes control to advance the injection timing of fuel injected from the injector when the time during which the rotation speed and the instruction value are within the predetermined range reaches the predetermined time.

7. a temperature sensor that is provided in the exhaust pipe downstream of the diesel oxidation catalyst and that measures a temperature inside the exhaust pipe; 6. The exhaust gas recirculation device according to claim 5, wherein the control device further executes control to stop a pre-injection that is performed before a main injection when the time during which the rotation speed and the indication value are within the predetermined range reaches the predetermined time and the temperature measured by the temperature sensor is less than a threshold value.

8. the predetermined time is a first predetermined time, 6. The exhaust gas recirculation device according to claim 5, wherein the control device, after executing the control to prohibit the learning, executes control to resume the learning when the time during which the rotation speed and the instruction value are outside the predetermined range reaches a second predetermined time.

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