Exhaust gas recirculation device

Abstract

To provide an exhaust gas recirculation device capable of restoring the combustion from abnormal combustion to normal combustion in the event of an accidental fire when controlling opening of flow rate adjusting means by the learning using an NOx sensor.SOLUTION: An exhaust gas recirculation device 3 includes: an exhaust pipe 26; a diesel oxidation catalyst 261; a temperature sensor 54 for measuring the temperature inside the exhaust pipe 26; an NOx sensor 53 for measuring NOx concentration inside the exhaust pipe 26; an exhaust gas recirculation pipe 27 for guiding exhaust recirculation gas to an induction system; flow rate adjusting means 28 for adjusting a flow rate of the exhaust recirculation gas; and a control device 4 for learning a correction value derived on the basis of a deviation between a target value of the NOx concentration and an actually measured value of the NOx concentration, and executing control to set a final opening of the flow rate adjusting means 28 on the basis of the learned learning value and the basic opening of the flow rate adjusting means 28, and executing control to lower the final opening of the flow rate adjusting means 28 when the temperature measured by the temperature sensor 54 becomes a predetermined temperature or higher.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an exhaust gas recirculation device.

Background Art

[0002] As a means for reducing nitrogen oxides (NOx) contained in engine exhaust gas, exhaust gas recirculation (EGR) is generally known. An exhaust gas recirculation device recirculates a part of the exhaust flowing through the engine exhaust system as exhaust reflux gas (i.e., EGR gas) to the engine intake system and mixes the exhaust reflux gas with the fresh intake air. Compared with the case where the exhaust gas recirculation device is not provided, the exhaust gas recirculation device can lower the combustion temperature in the cylinder and suppress the generation of NOx.

[0003] However, when the exhaust reflux gas is mixed with the fresh intake air, the oxygen concentration of the air inhaled into the cylinder decreases compared with the case where the exhaust reflux gas is not mixed with the fresh intake air. Therefore, there is a risk of misfire. In addition, misfire may occur when the intake air temperature is low and when the cetane number of the fuel is low. Furthermore, misfire may occur due to individual differences in various components such as injectors.

[0004] Here, Patent Document 1 discloses a control device for an in-cylinder injection type internal combustion engine that estimates the occurrence of misfire by focusing on the fact that when misfire occurs, the engine rotational speed (and thus the angular velocity of the crankshaft) instantaneously decreases only during misfire. Further, Patent Document 2 discloses a control method for a vehicle EGR system that determines misfire by detecting a change in the crank angle of the engine, similar to the technique described in Patent Document 1. Furthermore, Patent Document 3 discloses an EGR device for reducing NOx. The EGR device described in Patent Document 3 controls the EGR valve so that the measured NOx concentration by the NOx sensor becomes the target NOx concentration by determining the target NOx concentration according to the operating state only when the change amount per unit time of the fuel injection amount of the engine is maintained within an allowable range.

[0005] However, when the exhaust gas recirculation device performs learning based on the target value of the NOx concentration and the measured value of the NOx concentration measured by the NOx sensor to set the opening degree of the EGR valve, if incorrect learning is performed, it is difficult to return the abnormal fuel that has caused misfire to normal combustion. Further, as described in Patent Document 1 and Patent Document 2, when misfire occurs, the operating state of the engine becomes unstable, such as a large fluctuation in the engine rotation speed (i.e., the angular velocity of the crankshaft). Therefore, the EGR device as described in Patent Document 3 cannot execute the control of the EGR valve based on the detection value of the NOx sensor, and there are cases where it is difficult to return the abnormal fuel that has caused misfire to normal combustion.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust gas recirculation device that can return abnormal combustion to normal combustion when misfire occurs in the case of controlling the opening degree of the flow rate adjusting means by learning using a NOx sensor.

Means for Solving the Problems

[0008] A first aspect of the present invention is an exhaust gas recirculation device that recirculates a part of the exhaust flowing through the exhaust system of an engine as exhaust recirculation gas to the intake system of the engine, comprising: an exhaust pipe provided in the exhaust system for guiding the exhaust; a diesel oxidation catalyst provided in the exhaust pipe; a temperature sensor provided downstream of the diesel oxidation catalyst in the exhaust pipe for measuring the temperature inside the exhaust pipe; a NOx sensor provided in the exhaust pipe for measuring the NOx concentration inside the exhaust pipe; an exhaust recirculation pipe connected to the exhaust pipe for guiding the exhaust recirculation gas to the intake system; flow rate adjusting means provided in the exhaust recirculation pipe for adjusting the flow rate of the exhaust recirculation gas flowing through the exhaust recirculation pipe; a control device that learns a correction value derived based on the deviation between the target value of the NOx concentration and the measured value of the NOx concentration measured by the NOx sensor, and executes control to set the final opening degree of the flow rate adjusting means based on the learned learned value and the basic opening degree of the flow rate adjusting means, and executes control to lower the final opening degree when the temperature measured by the temperature sensor becomes equal to or higher than a predetermined temperature. An exhaust gas recirculation device characterized by comprising:

[0009] A second aspect of the present invention is an exhaust gas recirculation device that recirculates a part of the exhaust flowing through the exhaust system of an engine as exhaust recirculation gas to the intake system of the engine, including an exhaust pipe provided in the exhaust system to guide the exhaust, a NOx sensor provided in the exhaust pipe to measure the NOx concentration inside the exhaust pipe, an exhaust recirculation pipe connected to the exhaust pipe to guide the exhaust recirculation gas to the intake system, a flow rate adjustment means provided in the exhaust recirculation pipe to adjust the flow rate of the exhaust recirculation gas flowing through the exhaust recirculation pipe, a rotation sensor that detects the rotational speed of the engine and outputs a first detection signal regarding the rotational speed, an accelerator opening sensor that detects the accelerator opening and outputs a second detection signal regarding the accelerator opening, sets an instruction 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 measured value of the NOx concentration measured by the NOx sensor, and executes control to set the 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 lower the final opening when the fluctuation range of the instruction value exceeds a predetermined range. An exhaust gas recirculation device characterized by comprising a control device.

Effects of the Invention

[0010] According to the present invention, when controlling the opening of the flow rate adjustment means by learning using a NOx sensor, it is possible to provide an exhaust gas recirculation device that can return abnormal combustion to normal combustion when misfire occurs.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Mode for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the embodiments described below are preferred specific examples of the present invention, and thus various technically preferable limitations are imposed. However, the scope of the present invention is not limited to these aspects unless there is a description to specifically limit the present invention in the following description. Also, in each drawing, the same reference numerals are assigned to the same components, and detailed descriptions are appropriately omitted.

[0013] FIG. 1 is a schematic diagram showing an engine according to the present embodiment. FIG. 2 is a block diagram showing the main configuration of an exhaust gas recirculation device according to the present embodiment.

[0014] The engine 2 according to this embodiment is an internal combustion engine and is a naturally aspirated small 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 about 500 cc. However, the displacement is not limited to about 500 cc. The timing deviation between the combustion process of the first cylinder 241 and the combustion process of the second cylinder 242 is, for example, 180 degrees as the angle of the crankshaft. However, the timing deviation between the combustion process of the first cylinder 241 and the combustion process of the second cylinder 242 is not limited to this, and may be 360 degrees as the angle of the crankshaft. Note that the engine 2 according to this embodiment does not include a turbocharger for supercharging.

[0015] 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) of the cylinder head. The second cylinder 242 is connected to the second branch pipe 222 via an intake port of the cylinder head. The exhaust manifold 25 is connected to the cylinder head and the exhaust pipe 26. Specifically, the exhaust manifold 25 is connected to the first cylinder 241 and the second cylinder 242 via the exhaust ports of the cylinder head. Note that the exhaust pipe 26 may be included in the exhaust gas recirculation device 3 described later.

[0016] Further, the engine 2 includes a rail 23, a first injector 231, and a second injector 232. The rail 23 is formed in a cylindrical shape and distributes the 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.

[0017] The first injector 231 is attached to the rail 23 and is provided so as to protrude toward the combustion chamber formed in the upper part of the first cylinder 241. The first injector 231 opens and closes a needle valve, for example, by a solenoid based on a signal transmitted from the control device 4, and injects the fuel supplied from the rail 23 into the combustion chamber formed in the upper part of the first cylinder 241 through an injection hole (not shown). Examples of the control device 4 include an electronic control unit (ECU).

[0018] The second injector 232 is attached to the rail 23 and is provided so as to protrude toward the combustion chamber formed in the upper part of the second cylinder 242. The second injector 232 opens and closes a needle valve, for example, by a solenoid based on a signal transmitted from the control device 4, and injects the fuel supplied from the rail 23 into the combustion chamber formed in the upper part of the second cylinder 242 through an injection hole.

[0019] 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 regarding the fuel pressure to the control device 4.

[0020] As shown by the arrow A1 in FIG. 1, the fresh intake air (i.e., the intake air) passes through the intake pipe 21, passes through the air cleaner 211 provided in the intake pipe 21, and is guided to the intake manifold 22. The intake air guided to the intake manifold 22 is distributed to the first branch pipe 221 and the second branch pipe 222, and is guided to the first cylinder 241 through the first branch pipe 221 and to the second cylinder 242 through the second branch pipe 222.

[0021] The exhaust gas discharged from the first cylinder 241 and the second cylinder 242 passes through the exhaust manifold 25 and is led to the exhaust pipe 26. The exhaust gas led 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 the SOF (soluble organic fraction), CO (carbon monoxide), and HC (hydrocarbon) in the PM (particulate matter) contained in the exhaust gas. As shown by the arrow A2 in FIG. 1, the exhaust gas that has passed through the diesel oxidation catalyst 261 is discharged to the outside of the engine 2 through the exhaust pipe 26. Note that the diesel oxidation catalyst 261 may be included in the exhaust gas recirculation device 3 described later.

[0022] Furthermore, the engine 2 includes an exhaust gas recirculation device 3. The exhaust gas recirculation device 3 recirculates a part of the exhaust gas flowing through the exhaust system of the engine 2 as exhaust reflux gas to the intake system of the engine 2 to reduce nitrogen oxides (NOx) contained in the exhaust gas.

[0023] The exhaust gas recirculation device 3 according to the present embodiment includes an exhaust reflux pipe 27 and a flow rate adjusting means 28. As shown in FIG. 1, the exhaust reflux pipe 27 is connected to the exhaust pipe 26 and the intake manifold 22, and guides a part of the exhaust gas flowing through the exhaust pipe 26 to the intake manifold 22 as exhaust reflux gas. The flow rate adjusting means 28 is, for example, called an EGR valve and is provided in the exhaust reflux pipe 27. The flow rate adjusting means 28 adjusts the flow rate of the exhaust reflux gas flowing through the exhaust reflux pipe 27 based on a signal transmitted from the control device 4.

[0024] Also, as shown in FIGS. 1 and 2, the exhaust gas recirculation device 3 includes a control device 4, a rotation sensor 51, a NOx sensor 53, a temperature sensor 54, and an accelerator opening sensor 56. Note that the cam angle sensor 52, the pressure sensor 55, and the injector (that is, 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 and may be included in the engine 2.

[0025] As shown in FIG. 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 has a function as a CPU (Central Processing Unit), reads out the program 421 stored in the storage unit 42, and executes various calculations and processes.

[0026] The arithmetic processing unit 41 receives, via the communication unit 43, a detection signal regarding the rotational speed ES of the engine 2 output from the rotation sensor 51. The detection signal regarding the rotational speed ES of the engine 2 is an example of the "first detection signal" of the present invention. The rotation sensor 51, also called a crank angle sensor, detects the reference position and rotation angle of the crankshaft of the engine 2, detects the rotational speed ES of the engine 2, and outputs a detection signal regarding the reference position and rotation angle of the crankshaft, as well as a detection signal regarding the rotational speed ES of the engine 2, to the control device 4.

[0027] The arithmetic processing unit 41 receives, via the communication unit 43, a detection signal regarding 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 regarding the reference position and rotation angle of the camshaft of the engine 2 to the control device 4.

[0028] The arithmetic processing unit 41 receives, via the communication unit 43, a detection signal regarding the measured 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. Further, the NOx sensor 53 outputs a detection signal regarding the measured value of the measured NOx concentration to the control device 4.

[0029] The arithmetic processing unit 41 receives, via the communication unit 43, a detection signal regarding the temperature inside the exhaust pipe 26 output from the temperature sensor 54. As shown in FIG. 1, the temperature sensor 54 is provided downstream of the diesel oxidation catalyst 261 in the exhaust pipe 26 and measures the temperature inside the exhaust pipe 26. Further, the temperature sensor 54 outputs a detection signal regarding the measured temperature inside the exhaust pipe 26 to the control device 4.

[0030] The arithmetic processing unit 41 receives, via the communication unit 43, a signal regarding the fuel pressure output from the pressure sensor 55. The pressure sensor 55 is as described above.

[0031] The arithmetic processing unit 41 receives, via the communication unit 43, a detection signal regarding the accelerator opening output from the accelerator opening sensor 56. The detection signal regarding the accelerator opening is an example of the "second detection signal" of the present invention. The accelerator opening sensor 56 detects the accelerator opening and outputs a detection signal regarding the accelerator opening to the control device 4.

[0032] Based on the detection signal regarding the engine speed ES output from the rotation sensor 51 and the detection signal regarding the accelerator opening output from the accelerator opening sensor 56, the arithmetic processing unit 41 sets, for example, an instruction value FQD for the fuel injection amount using a governor map (not shown) stored in the storage unit 42. The arithmetic processing unit 41 outputs, via the communication unit 43, a signal regarding the set instruction value FQD for the fuel injection amount to the first injector 231 and the second injector 232. The first injector 231 and the second injector 232 inject the fuel supplied from the rail 23 into the combustion chamber based on the instruction value FQD for the fuel injection amount output from the arithmetic processing unit 41 via the communication unit 43.

[0033] The arithmetic processing unit 41 sets the opening degree of the flow rate adjusting means 28, and outputs a signal regarding the opening degree of the flow rate adjusting means 28 to the flow rate adjusting means 28 via the communication unit 43. Details of the control for the arithmetic processing unit 41 to set the opening degree of the flow rate adjusting means 28 will be described later. The flow rate adjusting means 28 opens and closes the valve based on the signal regarding the opening degree output from the arithmetic processing unit 41 via the communication unit 43, and adjusts the flow rate of the exhaust reflux gas flowing through the exhaust reflux pipe 27.

[0034] The storage unit 42 stores (stores) a program 421, a NOx concentration target value map 422, an addition value map 423, a basic opening degree map 424, a gain low speed map 425, a gain medium speed map 426, and a gain high speed map 427. Further, the storage unit 42 stores result values obtained when the arithmetic processing unit 41 performs calculations and processes, and learning values learned by the arithmetic processing unit 41. Examples of the storage unit 42 include a ROM (Read Only Memory) and a RAM (Random Access Memory). Note that the storage unit 42 may be an external storage device connected to the control device 4.

[0035] Examples of the program 421 include an arithmetic program used when the arithmetic processing unit 41 performs calculations and processes, a sequence program used when the arithmetic processing unit 41 executes the control described later, 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 pre-stored and distributed in a storage medium readable by the arithmetic processing unit 41, or may be downloaded to the control device 4 via a network.

[0036] The NOx concentration target value map 422 is map data showing the relationship between the rotational speed ES (rpm) of the engine 2, the indicated value FQD (mm 3 / st) of the fuel injection amount, and the target value of the NOx concentration, and is used when the arithmetic processing unit 41 sets the target value of the NOx concentration. The addition value map 423 is map data showing the relationship between the deviation between the target value of the NOx concentration and the measured value of the NOx concentration measured by the NOx sensor, and the addition value for the deviation integration described later, and is used when the arithmetic processing unit 41 sets the addition value for the deviation integration. The "deviation integration" in the present embodiment is an example of the "learning value" of the present invention. Further, the "addition value" in the present embodiment is an example of the "correction value" of the present invention.

[0037] The basic opening map 424 is map data showing the relationship between the rotational speed ES of the engine 2, the indicated value FQD of the fuel injection amount, and the basic opening (%) of the flow rate adjusting means 28, and is used when the arithmetic processing unit 41 sets the basic opening of the flow rate adjusting means 28.

[0038] 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 rotational speed ES of the engine 2, the indicated value FQD of the fuel injection amount, and the integral control term gain described later, and are used when the arithmetic processing unit 41 sets the integral control term gain. The "integral control term gain" in the present embodiment is an example of the "gain" of the present invention.

[0039] Specifically, the low-speed gain map 425 is used when the arithmetic processing unit 41 sets the integral control term gain when the rotational speed ES of the engine 2 is low (for example, less than 1800 rpm). The medium-speed gain map 426 is used when the arithmetic processing unit 41 sets the integral control term gain when the rotational speed ES of the engine 2 is medium-speed (for example, 1800 rpm or more and less than 3100 rpm). The high-speed gain map 427 is used when the arithmetic processing unit 41 sets the integral control term gain when the rotational speed ES of the engine 2 is high-speed (for example, 3100 rpm or more). However, the rotational speeds ES of low speed (for example, less than 1800 rpm), medium speed (for example, 1800 rpm or more and less than 3100 rpm), and high speed (for example, 3100 rpm or more) are examples and are not limited to only these.

[0040] The above-described NOx concentration target value map 422, addition value map 423, basic opening degree map 424, gain low speed map 425, gain medium speed map 426, and gain high speed map 427 are not limited to map data showing each relationship, and may be mathematical formulas or distribution diagrams showing each relationship.

[0041] Next, the details of the control executed by the control device 4 of the present embodiment will be described with reference to the drawings. FIG. 3 is a block diagram for explaining the control in which the control device of the present embodiment derives deviation integration. FIG. 4 is a table exemplifying an example of the addition value map of the present embodiment. FIG. 5 is a block diagram for explaining the control in which the control device of the present embodiment sets the final opening degree of the flow rate adjusting means. FIG. 6 is a block diagram for explaining a modified example of the control in which the control device of the present embodiment sets the final opening degree of the flow rate adjusting means.

[0042] As shown in FIGS. 2 and 3, the arithmetic processing unit 41 sets the target value 61 of the NOx concentration using the NOx concentration target value map 422 based on the engine speed ES of the engine 2 and the instruction value FQD of the fuel injection amount. Subsequently, the arithmetic processing unit 41 receives a detection signal regarding the actually measured 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 actually measured value 62 of the NOx concentration. Specifically, the arithmetic processing unit 41 calculates the deviation 63 by subtracting the actually measured value 62 of the NOx concentration from the target value 61 of the NOx concentration.

[0043] Subsequently, the arithmetic processing unit 41 derives an addition value 64 for deviation integration using the addition value map 423 based on the calculated deviation 63. As described above with respect to FIGS. 1 and 2, the "deviation integration" of the present embodiment is an example of the "learning value" of the present invention. Further, the "addition value" of the present embodiment is an example of the "correction value" of the present invention.

[0044] As shown in the addition value map 423 shown in FIG. 4, when the deviation 63 is, for example, "5", the arithmetic processing unit 41 derives "-1" as the addition value 64 for the deviation integration. Thus, when the deviation 63 is a positive value, that is, when the measured value 62 of the NOx concentration is smaller than the target value 61 of the NOx concentration, the arithmetic processing unit 41 of the present embodiment sets a negative value as the addition value 64 for the deviation integration and controls the flow rate adjusting means 28 in the closing direction. However, the arithmetic processing unit 41 of the present embodiment does not necessarily set a negative value as the addition value 64 for the deviation integration when the deviation 63 is a positive value. As shown in the addition value map 423 shown in FIG. 4, when the deviation 63 is, for example, "1", the arithmetic processing unit 41 derives "0" as the addition value 64 for the deviation integration and executes control not to operate the flow rate adjusting means 28.

[0045] On the other hand, as shown in the addition value map 423 shown in FIG. 4, when the deviation 63 is, for example, "-5", the arithmetic processing unit 41 derives "1" as the addition value 64 for the deviation integration. Thus, when the deviation 63 is a negative value, that is, when the measured value 62 of the NOx concentration is larger than the target value 61 of the NOx concentration, the arithmetic processing unit 41 of the present embodiment sets a positive value as the addition value 64 for the deviation integration and controls the flow rate adjusting means 28 in the opening direction. However, the arithmetic processing unit 41 of the present embodiment does not necessarily set a positive value as the addition value 64 for the deviation integration when the deviation 63 is a negative value. As shown in the addition value map 423 shown in FIG. 4, when the deviation 63 is, for example, "-1", the arithmetic processing unit 41 derives "0" as the addition value 64 for the deviation integration and executes control not to operate the flow rate adjusting means 28.

[0046] Subsequently, as shown in FIG. 3, the arithmetic processing unit 41 learns the derived addition value 64 and stores it in the storage unit 42 as the deviation integration 65. Specifically, the arithmetic processing unit 41 derives the addition value 64 by the above-described control every predetermined time (for example, about 5 seconds), and adds the addition value 64 derived every predetermined time to the deviation integration 65 stored in the storage unit 42 every predetermined time, thereby updating the deviation integration 65 stored in the storage unit 42 every predetermined time.

[0047] 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 arithmetic processing unit 41 derives "2" as the addition 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 arithmetic processing unit 41 derives "1" as the addition value 64, and updates (i.e., sets) the deviation integral 65 to "3 (= 2 + 1)" by adding "1" to the "2" of the deviation integral 65 stored in the storage unit 42. When the deviation 63 after the further next predetermined time (for example, about 5 seconds) is "1", the arithmetic processing unit 41 derives "0" as the addition value 64, and updates (i.e., sets) the deviation integral 65 to "3 (= 3 + 0)" by adding "0" to the "3" of the deviation integral 65 stored in the storage unit 42.

[0048] Subsequently, as shown in FIGS. 2 and 5, the arithmetic processing unit 41 sets the basic opening degree 66 of the flow rate adjustment means 28 using the basic opening degree map 424 based on the rotational speed ES of the engine 2 and the indicated value FQD of the fuel injection amount. Note that the timing at which the arithmetic processing unit 41 sets the basic opening degree 66 of the flow rate adjustment means 28 is not limited to this timing, and it may be a previous timing (for example, the timing at which the arithmetic processing unit 41 sets the target value 61 of the NOx concentration (see FIG. 3)).

[0049] In addition, the arithmetic processing unit 41 derives the integral control term gain 67 using the gain map based on the rotational speed ES of the engine 2 and the indicated value FQD of the fuel injection amount. As described above with respect to FIGS. 1 and 2, the "integral control term gain" of the present embodiment is an example of the "gain" of the present invention. Note that the timing at which the arithmetic processing unit 41 sets the integral control term gain 67 is not limited to this timing, and it may be a previous timing (for example, the timing at which the arithmetic processing unit 41 sets the target value 61 of the NOx concentration (see FIG. 3)).

[0050] Subsequently, the arithmetic processing unit 41 calculates a value obtained by multiplying the deviation integral 65 stored in the storage unit 42 by the integral control term gain 67. Subsequently, the arithmetic 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 adjusting means 28, thereby setting the final opening (%) 68 of the flow rate adjusting means 28.

[0051] As a modification, as shown in FIG. 6, the arithmetic processing unit 41 of the present embodiment divides the deviation integral 65 according to the rotational speed ES of the engine 2 and stores it in the storage unit 42. Specifically, the arithmetic processing unit 41 calculates an average value 69 of the arithmetic cycle (for example, about 5 seconds) of the rotational speed ES of the engine 2. Subsequently, the arithmetic processing unit 41 stores in the storage unit 42 the deviation integral 65 to which the addition value 64 is added according to the average value 69 of the rotational speed ES of the engine 2.

[0052] For example, when the average value 69 of the rotational speed ES of the engine 2 is low (for example, less than 1800 rpm), the arithmetic processing unit 41 adds the addition value 64 to the deviation integral 651 for low speed stored in the storage unit 42 and updates the deviation integral 651 for low speed stored in the storage unit 42. Further, the arithmetic processing unit 41 derives the integral control term gain 671 for low speed using the gain map 425 for low speed based on the rotational speed ES of the engine 2 and the indicated value FQD of the fuel injection amount. Subsequently, the arithmetic processing unit 41 uses the deviation integral 651 for low speed according to the average value 69 of the rotational speed ES of the engine 2, and calculates a value obtained by multiplying the deviation integral 651 for low speed by the integral control term gain 671 for low speed. Subsequently, the arithmetic processing unit 41 adds the value obtained by multiplying the deviation integral 651 for low speed by the integral control term gain 671 for low speed to the basic opening 66 of the flow rate adjusting means 28, thereby setting the final opening 68 of the flow rate adjusting means 28.

[0053] For example, when the average value 69 of the rotational speed ES of the engine 2 is at medium speed (for example, 1800 rpm or more and less than 3100 rpm), the arithmetic processing unit 41 adds the addition value 64 to the deviation integration 652 for medium speed stored in the storage unit 42, and updates the deviation integration 652 for medium speed stored in the storage unit 42. Further, the arithmetic processing unit 41 derives the integration control term gain 672 for medium speed using the medium speed gain map 426 based on the rotational speed ES of the engine 2 and the indicated value FQD of the fuel injection amount. Subsequently, the arithmetic processing unit 41 uses the deviation integration 652 for medium speed according to the average value 69 of the rotational speed ES of the engine 2, and calculates a value obtained by multiplying the deviation integration 652 for medium speed by the integration control term gain 672 for medium speed. Subsequently, the arithmetic processing unit 41 sets the final opening degree 68 of the flow rate adjustment means 28 by adding the value obtained by multiplying the deviation integration 652 for medium speed by the integration control term gain 672 for medium speed to the basic opening degree 66 of the flow rate adjustment means 28.

[0054] For example, when the average value 69 of the rotational speed ES of the engine 2 is at high speed (for example, 3100 rpm or more), the arithmetic processing unit 41 adds the addition value 64 to the deviation integration 653 for high speed stored in the storage unit 42, and updates the deviation integration 653 for high speed stored in the storage unit 42. Further, the arithmetic processing unit 41 derives the integration control term gain 673 for high speed using the high speed gain map 427 based on the rotational speed ES of the engine 2 and the indicated value FQD of the fuel injection amount. Subsequently, the arithmetic processing unit 41 uses the deviation integration 653 for high speed according to the average value 69 of the rotational speed ES of the engine 2, and calculates a value obtained by multiplying the deviation integration 653 for high speed by the integration control term gain 673 for high speed. Subsequently, the arithmetic processing unit 41 sets the final opening degree 68 of the flow rate adjustment means 28 by adding the value obtained by multiplying the deviation integration 653 for high speed by the integration control term gain 673 for high speed to the basic opening degree 66 of the flow rate adjustment means 28.

[0055] Next, the conditions under which the arithmetic processing unit 41 of the present embodiment learns the addition value 64 and stores it in the storage unit 42 as the deviation integration 65 will be described with reference to the drawings. FIG. 7 is a block diagram for explaining the first condition for the arithmetic processing unit of the present embodiment to learn the correction value. FIG. 8 is a block diagram for explaining a second condition for the arithmetic processing unit of the present embodiment to learn correction values. FIG. 9 is a graph exemplifying the timing for the arithmetic processing unit of the present embodiment to learn correction values.

[0056] The arithmetic processing unit 41 of the present embodiment learns the addition value 64 and stores it in the storage unit 42 as the deviation integral 65 only when the first variation width of the rotational speed ES of the engine 2 within a predetermined time is maintained within a first predetermined range and the second variation width of the indicated value FQD of the fuel injection amount within a predetermined time is maintained within a second predetermined range. That is, the arithmetic processing unit 41 learns the addition 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, about 0 rpm or more and less than 30 rpm. The second predetermined range is, for example, 0 mm 3 / st or more and 2 mm 3 / st or less. However, the first predetermined range and the second predetermined range are not necessarily limited to the exemplified ranges.

[0057] The arithmetic processing unit 41 extracts a high-frequency component from the rotational speed ES of the engine 2 within a predetermined time, and determines whether the operating state of the engine 2 is stable based on the first variation width of the rotational speed ES of the engine 2. For example, as shown in FIG. 7, the arithmetic processing unit 41 determines whether the operating state of the engine 2 is stable based on the variation width of the high-frequency component extracted by passing the rotational speed ES of the engine 2 through the high-pass filter 71. Note that the arithmetic processing unit 41 may extract a predetermined frequency component from the rotational speed ES of the engine 2 within a predetermined time and determine whether the operating state of the engine 2 is stable based on the first variation width of the rotational speed ES of the engine 2, and it is not necessarily required to use the high-pass filter 71.

[0058] Further, the arithmetic processing unit 41 extracts a high-frequency component from the instruction value FQD of the fuel injection amount at a predetermined time, and determines whether the operating state of the engine 2 is stable based on the second variation width of the instruction value FQD of the fuel injection amount. For example, as shown in FIG. 8, the arithmetic processing unit 41 determines whether the operating state of the engine 2 is stable based on the variation width of the high-frequency component extracted when the instruction value FQD of the fuel injection amount passes through the high-pass filter 71. Note that the arithmetic processing unit 41 only needs to be able to extract a predetermined frequency component from the instruction value FQD of the fuel injection amount at a predetermined time and determine whether the operating state of the engine 2 is stable based on the second variation width of the instruction value FQD of the fuel injection amount, and does not necessarily need to use the high-pass filter 71.

[0059] Then, the arithmetic processing unit 41 learns the addition value 64 and stores it in the storage unit 42 as the deviation integral 65 only when the first variation width of the rotational speed ES of the engine 2 at a predetermined time is maintained within a first predetermined range and the second variation width of the instruction value FQD of the fuel injection amount at a predetermined time is maintained within a second predetermined range.

[0060] For example, at the timing T1 shown in FIG. 9, when the rotational speed ES of the engine 2 is low (for example, less than 1800 rpm), the first variation width of the rotational speed ES of the engine 2 at a predetermined time (see "variation of ES" shown in FIG. 9) is maintained within the first predetermined range, and the second variation width of the instruction value FQD of the fuel injection amount at a predetermined time (see "variation of FQD" shown in FIG. 9) is maintained within the second predetermined range. In this case, the arithmetic processing unit 41 learns the addition value 64 and stores it in the storage unit 42 as the deviation integral 65 (see "learning ON" shown in FIG. 9).

[0061] At timing T2 shown in FIG. 9, when the rotational speed ES of the engine 2 is medium speed (for example, 1800 rpm or more and less than 3100 rpm), the first fluctuation width of the rotational speed ES of the engine 2 in a predetermined time (see "ES variation" shown in FIG. 9) is maintained within a first predetermined range, and the second fluctuation width of the indicated value FQD of the fuel injection amount in a predetermined time (see "FQD variation" shown in FIG. 9) is maintained within a second predetermined range. In this case, the arithmetic processing unit 41 learns the addition value 64 and stores it in the storage unit 42 as the deviation integral 65 (see "Learning ON" shown in FIG. 9).

[0062] At timing T3 shown in FIG. 9, when the rotational speed ES of the engine 2 is high speed (for example, 3100 rpm or more), the first fluctuation width of the rotational speed ES of the engine 2 in a predetermined time (see "ES variation" shown in FIG. 9) is maintained within a first predetermined range, and the second fluctuation width of the indicated value FQD of the fuel injection amount in a predetermined time (see "FQD variation" shown in FIG. 9) is maintained within a second predetermined range. In this case, the arithmetic processing unit 41 learns the addition value 64 and stores it in the storage unit 42 as the deviation integral 65 (see "Learning ON" shown in FIG. 9).

[0063] On the other hand, when the first fluctuation width of the rotational speed ES of the engine 2 in a predetermined time is not maintained within the first predetermined range, or when the second fluctuation width of the indicated value FQD of the fuel injection amount in a predetermined time is not maintained within the second predetermined range, the arithmetic processing unit 41 of the present embodiment does not learn the addition value 46 and does not store the addition value 64 as a learned value in the storage unit 42. That is, when the operating state of the engine 2 is not stable, the arithmetic processing unit 41 does not learn the addition value 46 and does not store the addition value 64 as a learned value in the storage unit 42. In this case, the arithmetic processing unit 41 sets the final opening degree 68 of the flow rate adjusting means 28 using the deviation integral 65 stored in the storage unit 42 in the past (that is, the deviation integral 65 already stored in the storage unit 42).

[0064] For example, at timing T4 shown in FIG. 9, the first variation width of the rotational speed ES of the engine 2 at a predetermined time (see "variation of ES" shown in FIG. 9) is not maintained within the first predetermined range. In this case, the arithmetic processing unit 41 does not learn the addition value 46 and does not store the addition value 64 as a learned value in the storage unit 42 (see "learning OFF" shown in FIG. 9).

[0065] As described above, according to the engine 2 according to the present embodiment, the control device 4 of the exhaust gas recirculation device 3 does not set the final opening degree 68 of the flow rate adjusting means based only on the deviation 63 between the target value 61 of the NOx concentration and the measured value 62 of the NOx concentration. Instead, an addition value 64 is derived based on the deviation 63 between the target value 61 of the NOx concentration and the measured value 62 of the NOx concentration, and the derived addition value 64 is learned and stored in the storage unit 42 as a deviation integral 65. Then, the control device 4 sets the final opening degree 68 of the flow rate adjusting means 28 based on the deviation integral 65 stored in the storage unit 42 and the basic opening degree 66 of the flow rate adjusting means 28. Specifically, the control device 4 multiplies the deviation integral 65 stored in the storage unit 42 by the integral control term gain 67 derived based on the rotational speed ES of the engine 2 and the instruction value FQD of the fuel injection amount, and adds the result to the basic opening degree 66 of the flow rate adjusting means 28 to set the final opening degree 68 of the flow rate adjusting means 28. Thereby, compared with the case where the exhaust gas recirculation device 3 sets the final opening degree 68 of the flow rate adjusting means 28 based only on the deviation 63 between the target value 61 of the NOx concentration and the measured value 62 of the NOx concentration, the exhaust gas recirculation device 3 can set the final opening degree 68 of the flow rate adjusting means 28 so that the measured value 62 of the NOx concentration becomes the target value 61 of the NOx concentration and control the flow rate of the exhaust reflux gas.

[0066] Further, the control device 4 updates the deviation integral 65 stored in the storage unit 42 every predetermined time by adding the addition value 64 derived every predetermined time to the deviation integral 65. Thereby, even in the case of the NOx sensor 53 with a slow response speed, the control device 4 can use the deviation integral 65 stored in the storage unit 42 to set the final opening degree 68 of the flow rate adjusting means 28 with high accuracy and control the flow rate of the exhaust reflux gas.

[0067] That is, generally, the time required for the flow sensor to make a measurement is about several milliseconds, while the time required for the NOx sensor to make a measurement is about several seconds (about 100 times that of the flow sensor). When the control device operates the opening degree of the EGR valve based on the measured value of the NOx sensor, it takes about several seconds until the NOx concentration as a result of that operation is measured. Then, rather than operating to suddenly change the opening degree of the EGR valve, the control device can more easily grasp the change in the NOx concentration as a result of the operation by operating to gradually change it, so that the flow rate of the EGR gas can be controlled more accurately. This is one of the reasons why the control device 4 uses the deviation integration 65 (see FIG. 3). That is, by using the deviation integration 65, the control device 4 can perform an operation to gradually change the final opening degree 68 (see FIG. 5) of the flow rate adjustment means 28, and can more accurately control the flow rate of the exhaust gas recirculation gas.

[0068] Further, the control device 4 divides and stores the deviation integral 65 in the storage unit 42 according to the engine speed ES of the engine 2, and uses the deviation integral 65 (in this embodiment, the deviation integral 651 for low speed, the deviation integral 652 for medium speed, and the deviation integral 653 for high speed) stored in the storage unit 42 in a divided manner according to the engine speed ES of the engine 2. Further, the control device 4 derives the integral control term gain 67 (in this embodiment, the integral control term gain 671 for low speed, the integral control term gain 672 for medium speed, and the integral control term gain 673 for high speed) divided according to the engine speed ES of the engine 2 based on the engine speed ES of the engine 2 and the indicated value FQD of the fuel injection amount. Then, the control device 4 sets the final opening degree 68 of the flow rate adjusting means 28 by adding the value obtained by multiplying the deviation integral 65 stored in the storage unit 42 by the integral control term gain 67 to the basic opening degree 66 of the flow rate adjusting means 28. Thereby, the control device 4 selects and uses the deviation integral 65 according to the engine speed ES of the engine 2 in the operating regions of the engine 2 where the differential pressure between the intake pressure and the exhaust pressure is different (such as the high engine speed region and the low engine speed region), and the operating regions of the engine 2 where the NOx concentration is different (such as the high engine speed region and the low engine speed region), and derives the integral control term gain 67, 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. The final opening degree 68 of the flow rate adjusting means 28 can be set with high accuracy and the flow rate of the exhaust gas recirculation gas can be controlled.

[0069] Also, as described above with respect to FIGS. 7 to 9, the control device 4 learns the addition 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. Thereby, the control device 4 learns the addition value 64 only when the operating state of the engine 2 is stable even in the case of the NOx sensor 53 with a slow response speed, so that the actual measured value 62 of the NOx concentration becomes the target value 61 of the NOx concentration. The final opening degree 68 of the flow rate adjusting means 28 can be set with high accuracy and the flow rate of the exhaust gas recirculation gas can be controlled.

[0070] Also, as described above with reference to FIGS. 7 to 9, when the operating state of the engine 2 is not stable, the control device 4 does not learn the addition value 46 and does not store the addition value 64 as a learned value in the storage unit 42. Then, the control device 4 uses the deviation integral 65 stored in the storage unit 42 in the past, and sets the final opening degree 68 of the flow rate adjusting means 28 based on the deviation integral 65 and the basic opening degree 66 of the flow rate adjusting means 28. Thereby, even when the operating state of the engine 2 is not stable, the control device 4 uses the deviation integral 65 stored in the storage unit 42 in the past to set the final opening degree 68 of the flow rate adjusting means 28 so that the measured value 62 of the NOx concentration becomes the target value 61 of the NOx concentration, and can control the flow rate of the exhaust gas recirculation gas.

[0071] 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 storage unit 42 (see FIG. 2). Therefore, when the operating state of the engine 2 is not stable, the control device 4 can use the deviation integral 65 stored in the storage unit 42 in the past. Thereby, even when the operating state of the engine 2 is not stable, the control device 4 can control the flow rate of the exhaust gas recirculation gas.

[0072] Furthermore, the control device 4 learns the addition value 64 so that the final opening degree 68 of the flow rate adjusting means 28 becomes larger than the basic opening degree 66 of the flow rate adjusting means 28 as the operation time of the engine 2 elapses, and stores it in the storage unit 42 as the deviation integral 65. That is, the deviation integral 65 increases as the operation time of the engine 2 elapses. In other words, the deviation integral 65 at the time of factory shipment of the engine 2 is smaller than the deviation integral 65 after the operation time of the engine 2 has sufficiently elapsed.

[0073] Thereby, the control device 4 can suppress the flow rate of the exhaust gas recirculation gas at the time of factory shipment of the engine 2 and suppress the occurrence of misfires. Then, as the operation time of the engine 2 elapses, the control device 4 increases the flow rate of the exhaust gas recirculation gas, sets the final opening degree 68 of the flow rate adjusting means 28 so that the measured value 62 of the NOx concentration becomes the target value 61 of the NOx concentration, and can control the flow rate of the exhaust gas recirculation gas.

[0074] Next, the control related to misfire executed by the control device 4 of the present embodiment will be described with reference to the drawings. FIG. 10 is a flowchart for explaining a first specific example of the control related to misfire executed by the control device of the present embodiment.

[0075] When the control device 4 of the present embodiment executes the learning described above with respect to FIGS. 3 to 9 and sets the final opening degree 68 of the flow rate adjusting means 28, if incorrect learning is executed, it may be difficult to return the abnormal fuel at the time of misfire to normal combustion. Further, as described above with respect to FIGS. 7 to 9, the control device 4 of the present embodiment learns the addition 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. Therefore, even when the control device 4 executes correct learning, if misfire occurs, the operating state of the engine 2 becomes unstable due to abnormal combustion, and there is a possibility that the conditions for the control device 4 to execute learning are not satisfied. Then, it may be difficult to return the abnormal fuel at the time of misfire to normal combustion. Therefore, as described below, the control device 4 of the present embodiment executes control related to misfire.

[0076] That is, when misfire occurs, the HC (hydrocarbon) contained in the unburned fuel increases and burns in the diesel oxidation catalyst 261 (see FIG. 1). Therefore, when misfire occurs, the temperature measured by the temperature sensor 54 provided on the downstream side of the diesel oxidation catalyst 261 in the exhaust pipe 26 rises compared to the case where misfire does not occur.

[0077] Therefore, in step S11, the arithmetic processing unit 41 receives a detection signal regarding the temperature inside the exhaust pipe 26 output from the temperature sensor 54, and determines whether or not the measured temperature of the temperature sensor 54 is equal to or higher than a predetermined temperature. The predetermined temperature here is, for example, about 500°C. However, the predetermined temperature is not limited to about 500°C.

[0078] When the measured temperature of the temperature sensor 54 is equal to or higher than a predetermined temperature (step S11: YES), in step S12, the arithmetic processing unit 41 executes at least one of the control of multiplying the deviation integral 65 by a first predetermined coefficient D1 and the control of multiplying the target value 61 of the NOx concentration by a first predetermined coefficient E1.

[0079] The first predetermined coefficient D1 is less than “1.0” and is, for example, about “0.8”. Thereby, the deviation integral 65 becomes smaller as compared with the case where the arithmetic processing unit 41 does not multiply the deviation integral 65 by the first predetermined coefficient D1. Therefore, the final opening degree 68 of the flow rate adjusting means 28 described above with reference to FIGS. 5 to 6 becomes smaller. Thus, when the measured temperature of the temperature sensor 54 is equal to or higher than a predetermined temperature, the arithmetic processing unit 41 executes the control of multiplying the deviation integral 65 by the first predetermined coefficient D1 as one means, thereby controlling the flow rate adjusting means 28 in the closing direction. Note that the first predetermined coefficient D1 is not limited to about “0.8”.

[0080] The first predetermined coefficient E1 is greater than “1.0” and is, for example, about “1.2”. Thereby, the target value 61 of the NOx concentration becomes larger as compared with the case where the arithmetic processing unit 41 does not multiply the target value 61 of the NOx concentration by the first predetermined coefficient E1. Therefore, the deviation 63 described above with reference to FIGS. 3 to 4 becomes larger, and the added value 64 with respect to the deviation integral becomes smaller. Thereby, the deviation integral 65 becomes smaller. Therefore, the final opening degree 68 of the flow rate adjusting means 28 described above with reference to FIGS. 5 to 6 becomes smaller. Thus, when the measured temperature of the temperature sensor 54 is equal to or higher than a predetermined temperature, the arithmetic processing unit 41 executes the control of multiplying the target value 61 of the NOx concentration by the first predetermined coefficient E1 as one means, thereby controlling the flow rate adjusting means 28 in the closing direction. Note that the first predetermined coefficient E1 is not limited to about “1.2”.

[0081] Alternatively, in step S12, the arithmetic processing unit 41 may execute control to perform subtraction and addition instead of multiplication. In this case, the arithmetic processing unit 41 executes at least one of control to subtract a first predetermined coefficient D1 (positive value) from the deviation integral 65 and control to add a first predetermined coefficient E1 (positive value) to the target value 61 of the NOx concentration. Even in this case, the arithmetic processing unit 41 can control the flow rate adjusting means 28 in the closing direction by executing control to subtract the first predetermined coefficient D1 from the deviation integral 65 as one means. Also, the arithmetic processing unit 41 can control the flow rate adjusting means 28 in the closing direction by executing control to add the first predetermined coefficient E1 to the target value 61 of the NOx concentration as one means.

[0082] On the other hand, when the measured temperature of the temperature sensor 54 is not equal to or higher than the predetermined temperature (step S11: NO), in step S17, the arithmetic processing unit 41 determines whether or not the engine 2 has stopped. When the engine 2 has stopped (step S17: YES), the arithmetic processing unit 41 ends the control related to misfire. On the other hand, when the engine 2 has not stopped (step S17: NO), the arithmetic processing unit 41 executes the process described above with respect to step S11.

[0083] In step S13 following step S12, the arithmetic processing unit 41 determines whether or not a predetermined time has elapsed after executing the process described above with respect to step S12. The predetermined time here is, for example, about 60 seconds. However, the predetermined time is not necessarily limited to about 60 seconds. When the predetermined time has elapsed after the arithmetic processing unit 41 executes the process of step S12 (step S13: YES), in step S14, the arithmetic processing unit 41 determines again whether or not the measured temperature of the temperature sensor 54 is equal to or higher than the predetermined temperature. The process of step S14 is the same as the process described above with respect to step S11. On the other hand, when the predetermined time has not elapsed after the arithmetic processing unit 41 executes the process of step S12 (step S13: NO), the arithmetic processing unit 41 executes the process of step S13.

[0084] When the measured temperature of the temperature sensor 54 is equal to or higher than a predetermined temperature (step S14: YES), in step S15, the arithmetic processing unit 41 executes at least one of the controls of multiplying the deviation integration 65 by a second predetermined coefficient D2 and multiplying the target value 61 of the NOx concentration by a second predetermined coefficient E2.

[0085] The second predetermined coefficient D2 is less than “1.0” and is, for example, about “0.9”. Thus, in the same manner as the process described above with respect to step S12, the arithmetic processing unit 41 executes the control of multiplying the deviation integration 65 by the second predetermined coefficient D2 as one means, thereby controlling the flow rate adjusting means 28 in a further closing direction. Note that the second predetermined coefficient D2 is not limited to about “0.9”.

[0086] The second predetermined coefficient E2 is greater than “1.0” and is, for example, about “1.1”. Thus, in the same manner as the process described above with respect to step S12, the arithmetic processing unit 41 executes the control of multiplying the target value 61 of the NOx concentration by the second predetermined coefficient E2 as one means, thereby controlling the flow rate adjusting means 28 in a further closing direction. Note that the second predetermined coefficient E2 is not limited to about “1.1”.

[0087] Alternatively, in step S15, the arithmetic processing unit 41 may execute a control of performing subtraction and addition instead of multiplication. In this case, the arithmetic processing unit 41 executes at least one of the controls of subtracting a second predetermined coefficient D2 (positive value) from the deviation integration 65 and adding a second predetermined coefficient E2 (positive value) to the target value 61 of the NOx concentration. Even in this case, the arithmetic processing unit 41 can control the flow rate adjusting means 28 in a closing direction by executing the control of subtracting the second predetermined coefficient D2 from the deviation integration 65 as one means. Further, the arithmetic processing unit 41 can control the flow rate adjusting means 28 in a closing direction by executing the control of adding the second predetermined coefficient E2 to the target value 61 of the NOx concentration as one means.

[0088] When the arithmetic processing unit 41 executes control to subtract a predetermined coefficient from the deviation integral 65, the first predetermined coefficient D1 is equal to or greater than the second predetermined coefficient D2. Also, when the arithmetic processing unit 41 executes control to add a predetermined coefficient to the target value 61 of the NOx concentration, the first predetermined coefficient E1 is equal to or greater than the second predetermined coefficient E2.

[0089] On the other hand, when the measured temperature of the temperature sensor 54 is not equal to or higher than the predetermined temperature (step S14: NO), in step S16, the arithmetic processing unit 41 releases the first predetermined coefficient E1 and the second predetermined coefficient E2 related to the target value 61 of the NOx concentration. Step S17 following steps S15 and S16 is the same as step S17 following step S11, as described above.

[0090] As described above, according to this specific example, the control device 4 executes control to reduce the final opening degree 68 of the flow rate adjustment means 28 that adjusts the flow rate of the exhaust recirculation gas when the temperature measured by the temperature sensor 54 becomes equal to or higher than the predetermined temperature. As a result, the exhaust gas recirculation device 3 according to the present embodiment can return abnormal combustion to normal combustion when misfire occurs, even when controlling the final opening degree 68 of the flow rate adjustment means 28 by learning using the NOx sensor 53.

[0091] Also, regarding the predetermined coefficient that the arithmetic processing unit 41 multiplies the deviation integral 65 by, the first predetermined coefficient D1 (about "0.8" in this specific example) is less than or equal to the second predetermined coefficient D2 (about "0.9" in this specific example). Further, regarding the predetermined coefficient that the arithmetic processing unit 41 multiplies the target value 61 of the NOx concentration by, the first predetermined coefficient E1 (about "1.2" in this specific example) is greater than or equal to the second predetermined coefficient E2 (about "1.1" in this specific example). Alternatively, regarding the predetermined coefficient that the arithmetic processing unit 41 subtracts from the deviation integral 65, the first predetermined coefficient D1 is greater than or equal to the second predetermined coefficient D2. Further, regarding the predetermined coefficient that the arithmetic processing unit 41 adds to the target value 61 of the NOx concentration, the first predetermined coefficient E1 is greater than or equal to the second predetermined coefficient E2. Therefore, when the control device 4 reduces the final opening degree 68 of the flow rate adjustment means 28, it relatively significantly reduces the final opening degree 68 of the flow rate adjustment means 28 at the initial stage, and when the temperature measured by the temperature sensor 54 is still above the predetermined temperature, it relatively slightly reduces the final opening degree 68 of the flow rate adjustment means 28. Thereby, the control device 4 can surely reduce the final opening degree 68 of the flow rate adjustment means 28 while making use of the learned results, and can surely return the abnormal combustion to the normal combustion when misfire occurs.

[0092] FIG. 11 is a flowchart for explaining a second specific example of the control regarding misfire executed by the control device of the present embodiment. When misfire occurs, the fluctuation of the rotational speed ES of the engine 2 becomes larger compared to the case where misfire does not occur. When the fluctuation of the rotational speed ES of the engine 2 becomes larger, the fluctuation of the instruction value FQD of the fuel injection amount set by the control device 4 becomes larger.

[0093] Therefore, in step S21, the arithmetic processing unit 41 determines whether or not the variation range of the instruction value FQD of the fuel injection amount is equal to or greater than a predetermined range. When the variation range of the instruction value FQD of the fuel injection amount is equal to or greater than the predetermined range (step S21: YES), in step S22, the arithmetic processing unit 41 executes at least one of the control of multiplying the deviation integral 65 by a first predetermined coefficient D1 and the control of multiplying the target value 61 of the NOx concentration by a first predetermined coefficient E1. Alternatively, in step S22, the arithmetic processing unit 41 executes at least one of the control of subtracting a first predetermined coefficient D1 (positive value) from the deviation integral 65 and the control of adding a first predetermined coefficient E1 (positive value) to the target value 61 of the NOx concentration. The process of step S22 is the same as the process of step S12 described above with respect to FIG. 10.

[0094] On the other hand, when the variation range of the instruction value FQD of the fuel injection amount is not equal to or greater than the predetermined range (step S21: NO), in step S27, the arithmetic processing unit 41 determines whether or not the engine 2 has stopped. The process of step S27 is the same as the process of step S17 described above with respect to FIG. 10.

[0095] In step S23 following step S22, the arithmetic processing unit 41 determines whether or not a predetermined time has elapsed after executing the process described above with respect to step S22. The predetermined time here is, for example, about 1 second or more and 2 seconds or less. However, the predetermined time is not necessarily limited to about 1 second or more and 2 seconds or less. When the predetermined time has elapsed after the arithmetic processing unit 41 executes the process of step S22 (step S23: YES), in step S24, the arithmetic processing unit 41 determines again whether or not the variation range of the instruction value FQD of the fuel injection amount is equal to or greater than the predetermined range. The process of step S24 is the same as the process described above with respect to step S21. On the other hand, when the predetermined time has not elapsed after the arithmetic processing unit 41 executes the process of step S22 (step S23: NO), the arithmetic processing unit 41 executes the process of step S23.

[0096] When the variation range of the indicated value FQD of the fuel injection amount is equal to or greater than a predetermined range (step S24: YES), in step S25, the arithmetic processing unit 41 executes at least one of control for multiplying the deviation integration 65 by a second predetermined coefficient D2 and control for multiplying the target value 61 of the NOx concentration by a second predetermined coefficient E2. Alternatively, in step S25, the arithmetic processing unit 41 executes at least one of control for subtracting a second predetermined coefficient D2 (positive value) from the deviation integration 65 and control for adding a second predetermined coefficient E2 (positive value) to the target value 61 of the NOx concentration. The process of step S25 is the same as the process of step S15 described above with respect to FIG. 10.

[0097] On the other hand, when the variation range of the indicated value FQD of the fuel injection amount is less than the predetermined range (step S24: NO), in step S26, the arithmetic processing unit 41 releases a first predetermined coefficient E1 and a second predetermined coefficient E2 related to the target value 61 of the NOx concentration. The process of step S26 is the same as the process of step S16 described above with respect to FIG. 10. Steps S25 and S27 following step S26 are as described above with respect to step S27 following step S21.

[0098] As described above, according to the control of the present specific example, when the variation range of the indicated value FQD of the fuel injection amount becomes equal to or greater than a predetermined range, the control device 4 executes control to decrease the final opening degree 68 of the flow rate adjustment means 28 that adjusts the flow rate of the exhaust gas recirculation gas. Thereby, even when the exhaust gas recirculation device 3 according to the present embodiment controls the final opening degree 68 of the flow rate adjustment means 28 by learning using the NOx sensor 53, abnormal combustion can be restored to normal combustion when misfire occurs.

[0099] Also, the process of step S22 is the same as the process of step S12 described above with respect to FIG. 10. Further, the process of step S25 is the same as the process of step S15 described above with respect to FIG. 10. Therefore, the same effects as those described above with respect to FIG. 10 can be obtained.

[0100] The embodiments of the present invention have been described above. 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 manner different from the above.

Explanation of Reference Numerals

[0101] 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 reflux pipe, 28: Flow rate adjustment means, 41: Arithmetic processing unit, 42: Storage unit, 43: Communication unit, 46: Added value, 51: Rotation sensor, 52: Cam angle sensor, 53: NOx sensor, 54: Temperature sensor, 55: Pressure sensor, 56: Accelerator opening sensor, 61: Target value of NOx concentration, 62: Measured value of NOx concentration, 63: Deviation, 64: Added 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: Added value map, 424: Basic opening map, 425: Gain low speed map, 426: Gain medium speed map, 427: Gain high speed 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 part of the exhaust flowing through the exhaust system of an engine as exhaust recirculation gas to the intake system of the engine, an exhaust pipe provided in the exhaust system for guiding the exhaust, a diesel oxidation catalyst provided in the exhaust pipe, a temperature sensor provided downstream of the diesel oxidation catalyst in the exhaust pipe for measuring the temperature inside the exhaust pipe, a NOx sensor provided in the exhaust pipe for measuring the NOx concentration inside the exhaust pipe, an exhaust recirculation pipe connected to the exhaust pipe for guiding the exhaust recirculation gas to the intake system, flow rate adjusting means provided in the exhaust recirculation pipe for adjusting the flow rate of the exhaust recirculation gas flowing through the exhaust recirculation pipe, learning a correction value derived based on the deviation between the target value of the NOx concentration and the measured value of the NOx concentration measured by the NOx sensor, and executing control to set the final opening degree of the flow rate adjusting means based on the learned learned value and the basic opening degree of the flow rate adjusting means, and executing control to lower the final opening degree when the temperature measured by the temperature sensor becomes equal to or higher than a predetermined temperature; A control device, An exhaust gas recirculation device characterized by comprising.

2. The control device according to claim 1, wherein when the temperature measured by the temperature sensor becomes equal to or higher than a predetermined temperature, the final opening degree is lowered by multiplying the learned value by a predetermined coefficient. Exhaust gas recirculation device.

3. The predetermined coefficient is a first predetermined coefficient, After a predetermined time has elapsed since the control device multiplies the learned value by the first predetermined coefficient, when the temperature measured by the temperature sensor is still equal to or higher than the predetermined temperature, the learned value is multiplied by a second predetermined coefficient. The exhaust gas recirculation device according to claim 2, wherein the final opening degree is further reduced by multiplying.

4. The exhaust gas recirculation device according to claim 3, wherein the first predetermined coefficient is less than or equal to the second predetermined coefficient.

5. The control device according to claim 1, wherein when the temperature measured by the temperature sensor becomes equal to or higher than a predetermined temperature, the final opening degree is lowered by multiplying the target value by a predetermined coefficient. Exhaust gas recirculation device.

6. The predetermined coefficient is a first predetermined coefficient, The control device multiplies the target value by the first predetermined coefficient, and if the temperature measured by the temperature sensor is still equal to or higher than a predetermined temperature after a predetermined time has elapsed, further reduces the final opening degree by multiplying the target value by a second predetermined coefficient. The exhaust gas recirculation device according to claim 5, characterized in that.

7. The exhaust gas recirculation device according to claim 6, characterized in that the first predetermined coefficient is equal to or greater than the second predetermined coefficient.

8. The control device reduces the final opening degree by subtracting a predetermined coefficient from the learned value when the temperature measured by the temperature sensor becomes equal to or higher than a predetermined temperature. The exhaust gas recirculation device according to claim 1, characterized in that.

9. The predetermined coefficient is a first predetermined coefficient, After a predetermined time has elapsed since the control device subtracts the first predetermined coefficient from the learned value, if the temperature measured by the temperature sensor is still equal to or higher than a predetermined temperature, further reduces the final opening degree by subtracting a second predetermined coefficient from the learned value. The exhaust gas recirculation device according to claim 8, characterized in that.

10. The exhaust gas recirculation device according to claim 9, characterized in that the first predetermined coefficient is equal to or greater than the second predetermined coefficient.

11. The control device reduces the final opening degree by adding a predetermined coefficient to the target value when the temperature measured by the temperature sensor becomes equal to or higher than a predetermined temperature. The exhaust gas recirculation device according to claim 1, characterized in that.

12. The predetermined coefficient is a first predetermined coefficient, After a predetermined time has elapsed since the control device multiplies the target value by the first predetermined coefficient, if the temperature measured by the temperature sensor is still equal to or higher than a predetermined temperature, further reduces the final opening degree by adding a second predetermined coefficient to the target value. The exhaust gas recirculation device according to claim 5, characterized in that.

13. The exhaust gas recirculation device according to claim 12, characterized in that the first predetermined coefficient is equal to or greater than the second predetermined coefficient.

14. An exhaust gas recirculation device that recirculates a part of the exhaust flowing through the exhaust system of the engine as exhaust reflux gas to the intake system of the engine, An exhaust pipe provided in the exhaust system for guiding the exhaust, A NOx sensor provided in the exhaust pipe for measuring the NOx concentration inside the exhaust pipe, An exhaust reflux pipe connected to the exhaust pipe for guiding the exhaust reflux gas to the intake system, Flow rate adjustment means provided in the exhaust gas reflux pipe for adjusting the flow rate of the exhaust gas reflux flowing through the exhaust gas reflux pipe; A rotation sensor that detects the rotational speed of the engine and outputs a first detection signal related to the rotational speed; An accelerator opening sensor that detects the accelerator opening and outputs a second detection signal related to the accelerator opening; Based on the first detection signal and the second detection signal, a command value for the fuel injection amount is set, a correction value derived based on the deviation between the target value of the NOx concentration and the measured value of the NOx concentration measured by the NOx sensor is learned, and based on the learned value and the basic opening degree of the flow rate adjustment means, control is executed to set the final opening degree of the flow rate adjustment means, and when the fluctuation range of the command value becomes equal to or greater than a predetermined range, control is executed to lower the final opening degree; a control device; An exhaust gas recirculation device characterized by comprising the above.

15. The exhaust gas recirculation device according to claim 14, wherein when the fluctuation range of the command value becomes equal to or greater than a predetermined range, the control device reduces the final opening degree by multiplying the learned value by a predetermined coefficient.

16. The predetermined coefficient is a first predetermined coefficient, The exhaust gas recirculation device according to claim 15, wherein after a predetermined time has elapsed since the learned value is multiplied by the first predetermined coefficient, when the fluctuation range of the command value is still equal to or greater than a predetermined range, the control device further reduces the final opening degree by multiplying the learned value by a second predetermined coefficient.

17. The exhaust gas recirculation device according to claim 16, wherein the first predetermined coefficient is less than or equal to the second predetermined coefficient.

18. The exhaust gas recirculation device according to claim 14, wherein when the fluctuation range of the command value becomes equal to or greater than a predetermined range, the control device reduces the final opening degree by multiplying the target value by a predetermined coefficient.

19. The predetermined coefficient is a first predetermined coefficient, The exhaust gas recirculation device according to claim 18, wherein after a predetermined time has elapsed since the target value is multiplied by the first predetermined coefficient, when the fluctuation range of the command value is still equal to or greater than a predetermined range, the control device further reduces the final opening degree by multiplying the target value by a second predetermined coefficient.

20. The exhaust gas recirculation device according to claim 19, wherein the first predetermined coefficient is greater than or equal to the second predetermined coefficient.

21. The exhaust gas recirculation device according to claim 14, wherein when the fluctuation range of the instruction value becomes equal to or greater than a predetermined range, the control device reduces the final opening degree by subtracting a predetermined coefficient from the learning value.

22. The predetermined coefficient is a first predetermined coefficient, After a predetermined time has elapsed since the control device subtracts the first predetermined coefficient from the learning value, when the fluctuation range of the instruction value is still equal to or greater than the predetermined range, the control device subtracts a second predetermined coefficient from the learning value to further reduce the final opening degree. The exhaust gas recirculation device according to claim 21, characterized in that.

23. The exhaust gas recirculation device according to claim 22, wherein the first predetermined coefficient is equal to or greater than the second predetermined coefficient.

24. The exhaust gas recirculation device according to claim 14, wherein when the fluctuation range of the instruction value becomes equal to or greater than a predetermined range, the control device reduces the final opening degree by adding a predetermined coefficient to the target value.

25. The predetermined coefficient is a first predetermined coefficient, After a predetermined time has elapsed since the control device adds the first predetermined coefficient to the target value, when the fluctuation range of the instruction value is still equal to or greater than the predetermined range, the control device adds a second predetermined coefficient to the target value to further reduce the final opening degree. The exhaust gas recirculation device according to claim 24, characterized in that.

26. The exhaust gas recirculation device according to claim 25, wherein the first predetermined coefficient is equal to or greater than the second predetermined coefficient.

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