engine

Abstract

To perform, when a risk of accumulating deposits on an EGR valve is low, control for opening the EGR valve as much as possible to reduce emission of NOx contained in exhaust gas to external environment as much as possible.SOLUTION: An engine comprises a control unit for controlling an EGR valve. The control unit selects a predetermined control mode among at least a first mode, a second mode, and a third mode according to at least an engine rotation speed and a fuel injection amount, and controls the EGR valve in the selected control mode. The first mode is a control mode in which the EGR valve is fully closed. The second mode is a control mode in which the opening degree of the EGR valve is adjusted according to the operation state of the engine. The third mode is a control mode in which an ON period in which the opening degree of the EGR valve is adjusted according to the operation state of the engine and an OFF period in which the EGR valve is fully closed are repeated.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an engine equipped with an EGR (Exhaust Gas Recirculation) device. [Background technology]

[0002] In an engine equipped with an EGR device, if the amount of foreign matter (e.g., soot called deposits) adhering to the EGR valve increases, proper operation of the engine is hindered. Therefore, for example, in the engine disclosed in Patent Document 1, an estimated amount of deposits adhering to the EGR valve is compared with a threshold value, and if the estimated amount is equal to or greater than the threshold value, control is performed to stop the recirculation of part of the exhaust gas as EGR gas (EGR cut). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-057849 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, if the temperature of the EGR gas is not low enough to cause deposits to build up on the EGR valve, the risk of deposits building up on the EGR valve is low. In the control described in Patent Document 1, even if the risk of deposits building up on the EGR valve is low, EGR cut is performed when the estimated amount of deposits exceeds a threshold. In this case, EGR gas is not recirculated to the intake side, which raises concerns about increased release of NOx contained in exhaust gas into the external environment (NOx emissions).

[0005] The present invention has been made to solve the above problems, and its purpose is to provide an engine that can control the EGR valve to open as much as possible when the risk of deposits accumulating in the EGR valve is low, thereby minimizing the release of NOx contained in exhaust gas into the external environment. [Means for solving the problem]

[0006] An engine according to one aspect of the present invention is an engine including an EGR device that recirculates a portion of exhaust gas discharged from a cylinder head as EGR gas to an intake pipe that supplies gas to the cylinder head, the EGR device having an EGR valve that adjusts the amount of recirculation of the EGR gas, and further including a control unit that controls the EGR valve, the control unit selecting a predetermined control mode from at least a first mode, a second mode, and a third mode depending on at least the engine speed and the fuel injection amount, and controlling the EGR valve in the selected control mode, the first mode being a control mode in which the EGR valve is fully closed, the second mode being a control mode in which the opening degree of the EGR valve is adjusted depending on the operating state of the engine, and the third mode being a control mode in which an on period in which the opening degree of the EGR valve is adjusted depending on the operating state of the engine and an off period in which the EGR valve is fully closed are repeated. [Effects of the Invention]

[0007] When the risk of deposits accumulating in the EGR valve is low, for example, by selecting the third mode, the EGR valve is controlled to be as open as possible, thereby minimizing the release of NOx contained in the exhaust gas into the external environment. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an explanatory diagram schematically illustrating a general configuration of an engine according to an embodiment of the present invention; [Figure 2] FIG. 2 is a block diagram showing the configuration of the main parts of the engine. [Figure 3]10 is a graph schematically showing a threshold value of the fuel injection amount set according to the engine speed. [Figure 4] FIG. 4 is an explanatory diagram showing details of a third mode, which is one of the control modes of the EGR valve. [Figure 5] 4 is a flowchart showing the flow of an operation for controlling the EGR valve. [Figure 6] FIG. 10 is an explanatory diagram schematically showing the relationship between the temperature of EGR gas and the duty ratio when the EGR valve is controlled in the third mode. [Figure 7] FIG. 10 is an explanatory diagram schematically showing the relationship between the number of initialization steps and the duty ratio when the EGR valve is controlled in the third mode. [Figure 8] 6 is a graph schematically showing a change in the first threshold value due to the transition of the control mode. [Figure 9] 6 is a graph schematically showing a change in the second threshold value due to the transition of the control mode. DETAILED DESCRIPTION OF THE INVENTION

[0009] The following describes an embodiment of the present invention with reference to the drawings.

[0010] [1. Engine configuration] The configuration of the engine of this embodiment will be described below. Fig. 1 is an explanatory diagram that schematically shows the general configuration of engine 1 of this embodiment. Fig. 2 is a block diagram that shows the configuration of the main parts of engine 1. Engine 1 is, for example, a diesel engine, and is installed in a work vehicle (work machine), agricultural machine, ship, etc.

[0011] The engine 1 includes, as components of its intake system, an intake pipe 2 and an intake manifold 3. The intake pipe 2 draws in gas from the outside and supplies it to the intake manifold 3.

[0012] The intake manifold 3 divides the gas supplied from the intake pipe 2 into a number of separate streams corresponding to the number of cylinders (for example, four in FIG. 1 ), and supplies each to a cylinder head 4. The cylinder head 4 has a cylinder head cover (not shown) that covers each cylinder, and an injector 5 (fuel injection device) provided corresponding to each combustion chamber 4a of the cylinder. The injector 5 injects fuel stored at high pressure in a common rail 6 into the combustion chamber 4a of each cylinder at a predetermined timing. Each cylinder is provided with a piston that slides back and forth within the combustion chamber 4a and rotates the crankshaft via a connecting rod.

[0013] The injector 5 is controlled by an ECU (engine control unit) 20. The ECU 20 is a control unit that controls the operation of each part of the engine 1.

[0014] The engine 1 includes an exhaust manifold 7, an exhaust pipe 8, and an exhaust gas purification device 9 as components of its exhaust system.

[0015] The exhaust manifold 7 collects gases (exhaust gases) generated in the multiple combustion chambers 4a. An exhaust manifold temperature sensor 7a is provided in the exhaust manifold 7. The exhaust manifold temperature sensor 7a detects the temperature of the exhaust manifold 7 (which is approximate to the temperature of the exhaust gases in the exhaust manifold 7). Temperature information detected by the exhaust manifold temperature sensor 7a is output to the ECU 20.

[0016] A portion of the gas that has passed through the exhaust manifold 7 is supplied to an EGR (Exhaust Gas Recirculation) device 10 (described later), and the remaining gas is supplied to an exhaust gas purification device 9 via an exhaust pipe 8 .

[0017] The exhaust gas purification device 9 is a device that purifies and discharges exhaust gas, and is also called a DPF (Diesel Particulate Filter). The exhaust gas purification device 9 includes an oxidation catalyst 9a and a filter 9b. The oxidation catalyst 9a is a catalyst for oxidizing (burning) unburned fuel, carbon monoxide, nitrogen monoxide, etc. contained in the exhaust gas, and is made of platinum or the like. The filter 9b is configured as, for example, a wall-flow type filter, and collects PM (Particulate Matter) contained in the exhaust gas treated by the oxidation catalyst 9a.

[0018] The engine 1 of this embodiment is equipped with an EGR device 10. The EGR device 10 is an exhaust gas recirculation device that returns a portion of the exhaust gas discharged from the cylinder head 4 as EGR gas to the intake pipe 2 that supplies gas to the cylinder head 4. The EGR device 10 has an EGR pipe 11, an EGR cooler 12, and an EGR valve 13.

[0019] The EGR cooler 12 cools the exhaust gas (EGR gas) supplied from the exhaust manifold 7 via the EGR pipe 11. The EGR valve 13 changes the amount of EGR gas supplied from the EGR cooler 12 to the intake pipe 2. In other words, the EGR valve 13 adjusts the amount of EGR gas supplied from the EGR cooler 12 that is returned to the intake pipe 2. By mixing the exhaust gas with the gas taken into the intake manifold 3, the amount of oxygen in the taken gas is reduced, thereby lowering the combustion temperature. This reduces the generation of nitrogen oxides known as NOx, and reduces the release of NOx contained in the exhaust gas into the external environment (NOx emissions).

[0020] The EGR device 10 further includes an EGR gas temperature detection sensor 14 and a valve position sensor 15. The EGR gas temperature detection sensor 14 detects the temperature of the EGR gas flowing through the EGR valve 13.

[0021] The valve position sensor 15 detects the position of the EGR valve 13. For example, in a configuration in which the opening of the EGR valve 13 (the amount of recirculated EGR gas) is adjusted by unidirectionally translating the EGR valve 13, the valve position sensor 15 detects the position (initial position) of the EGR valve 13 at engine start as the number of initialization steps. When deposits (e.g., soot) accumulate in the EGR valve 13, the number of initialization steps changes (e.g., increases). Therefore, the valve position sensor 15 detects the initial position (number of initialization steps) of the EGR valve 13 and outputs the detection result (detection signal) to the ECU 20, whereby the ECU 20 can recognize the amount of deposits adhering to the EGR valve 13 based on the detection signal.

[0022] As shown in FIG. 2, the engine 1 further includes an engine speed sensor 16. The engine speed sensor 16 detects the rotation speed of the crankshaft of the engine 1 as the rotation speed (actual rotation speed) of the engine 1. Information on the engine speed detected by the engine speed sensor 16 is output to the ECU 20. This allows the ECU 20 to recognize the operating state of the engine 1 based on the engine speed. For example, the ECU 20 can recognize based on the engine speed whether the engine 1 is stopped, starting (cranking), or operating normally.

[0023] The engine 1 further includes an accelerator opening sensor 17. The accelerator opening sensor 17 is configured, for example, by an accelerator pedal position sensor. The accelerator pedal position sensor detects the position of the accelerator pedal, i.e., the amount of depression of the accelerator pedal, as the accelerator opening. Information about the accelerator opening detected by the accelerator opening sensor 17 is output to the ECU 20. This allows the ECU 20 to recognize the target rotation speed of the engine 1 based on the accelerator opening. In other words, the target rotation speed of the engine 1 is determined according to the accelerator opening.

[0024] In this embodiment, the ECU 20 selects a predetermined control mode from a plurality of control modes according to at least the engine speed (actual speed) and the fuel injection amount, and controls the EGR valve 13 in the selected control mode. Here, the above fuel injection amount refers to the fuel injection amount (target injection amount) for realizing the target engine speed of the engine 1. The ECU 20 performs feedback control to adjust the target injection amount so that the engine speed approaches the target speed. Further, the ECU 20 has a map of the relationship between the fuel injection amount, the energization time to the injector 5, and the common rail pressure, and this map is calibrated after measuring the actual fuel injection amount. Therefore, the above target injection amount can be regarded as the same as the actual fuel injection amount.

[0025] In addition to the function of controlling the EGR valve 13, the above ECU 20 also has a function as a timing unit for measuring time, and a function as a storage unit for storing the control program of the ECU 20, various maps, and the like.

[0026] 〔2. Control of EGR Valve〕 Hereinafter, the details of the control of the EGR valve 13 by the ECU 20 will be described. FIG. 3 schematically shows the threshold values of the fuel injection amount set according to the engine speed. Here, the threshold values of the fuel injection amount are set as the first threshold Th1 and the second threshold Th2 in ascending order. That is, at the same engine speed, Th1 < Th2. As shown in the figure, both the first threshold Th1 and the second threshold Th2 change according to the engine speed. Specifically, the first threshold Th1 and the second threshold Th2 decrease as the engine speed increases. Note that the changes in the first threshold Th1 and the second threshold Th2 shown in FIG. 3 are only examples and are not limited thereto.

[0027] In this embodiment, as control modes of the EGR valve 13, there are three control modes: the first mode M1, the second mode M2, and the third mode M3.

[0028] The first mode M1 is a control mode that fully closes the EGR valve 13. When the ECU 20 selects the first mode M1 and controls the EGR valve 13, the EGR valve 13 is fully closed, thereby suppressing the accumulation of deposits in the EGR valve 13.

[0029] The second mode M2 ​​is a control mode that adjusts the opening of the EGR valve 13 in accordance with the operating state of the engine 1, and is the same as the normal control that is performed when the engine 1 is operating. When the ECU 20 selects the second mode M2 ​​and controls the EGR valve 13, the opening of the EGR valve 13 is adjusted in accordance with the operating state of the engine 1, thereby reducing the generation of NOx contained in the exhaust gas and making it possible to reduce NOx emissions.

[0030] FIG. 4 is an explanatory diagram showing details of the third mode M3. The third mode M3 is a control mode in which an on period P1 and an off period P2 are repeated at a predetermined ratio. Here, the on period P1 is a period in which the opening degree of the EGR valve 13 is adjusted according to the operating state of the engine 1. On the other hand, the off period P2 is a period in which the EGR valve 13 is fully closed. As shown in the figure, in the third mode M3, the on period P1 and the off period P2 are repeated at a predetermined cycle P. Note that, during the on period P1, the opening degree of the EGR valve 13 is adjusted according to the operating state of the engine 1, so the EGR valve 13 is not necessarily fully opened (the opening degree is 100%). The ratio of the on period P1 to the off period P2 in one cycle P is also referred to as the "duty ratio."

[0031] By the ECU 20 selecting the third mode M3 and controlling the EGR valve 13, the EGR valve 13 is fully closed during the off period P2 to suppress the buildup of deposits in the EGR valve 13, while the EGR valve 13 is opened during the on period P1 to reduce NOx emissions. In other words, it is possible to achieve both the suppression of the buildup of deposits in the EGR valve 13 and the reduction of NOx emissions.

[0032] FIG. 5 is a flowchart showing the flow of the operation for controlling the EGR valve 13. The control operation of the EGR valve 13 will be described below with reference to FIGS. 1 to 5. In the following, the target injection amount corresponding to the target rotation speed of the engine 1 recognized by the ECU 20 based on the accelerator opening detected by the accelerator opening sensor 17 is regarded as the actual fuel injection amount, and is simply referred to as the "fuel injection amount." Furthermore, the rotation speed of the engine 1 detected by the engine rotation speed sensor 16 is simply referred to as the "engine rotation speed."

[0033] First, the ECU 20 determines whether the fuel injection amount is equal to or less than a first threshold value Th1 (hereinafter simply referred to as "first threshold value Th1") corresponding to the engine speed (S1). If the fuel injection amount is equal to or less than the first threshold value Th1 (Yes in S1), the ECU 20 selects the first mode M1 as the control mode and controls the EGR valve 13 in the first mode M1 (S2).

[0034] On the other hand, if the fuel injection amount is greater than the first threshold value Th1 in S1 (No in S1), the ECU 20 determines whether the fuel injection amount is equal to or less than a second threshold value Th2 (hereinafter simply referred to as the "second threshold value Th2") corresponding to the engine speed (S3). At the same time in S3, the ECU 20 determines whether the amount of deposits on the EGR valve 13 is greater than a third threshold value Th3. As described above, the ECU 20 can recognize the amount of deposits based on the number of initialization steps detected by the valve position sensor 15. Furthermore, in S3, the ECU 20 determines whether the temperature of the EGR gas detected by the EGR gas temperature detection sensor 14 is equal to or less than a fourth threshold value Th4, and also determines whether the temperature of the exhaust manifold 7 detected by the exhaust manifold temperature sensor 7a is equal to or less than a fifth threshold value Th5.

[0035] If the determination in S3 is No, that is, for example, if the fuel injection amount is greater than the second threshold value Th2, the ECU 20 selects the second mode M2 ​​as the control mode and controls the EGR valve 13 in the second mode M2 ​​(S4). In addition, if the amount of deposits is equal to or less than the third threshold value Th3, if the temperature of the EGR gas is greater than the fourth threshold value Th4, or if the temperature of the exhaust manifold 7 is greater than the fifth threshold value Th5, the ECU 20 selects the second mode M2 ​​as the control mode and controls the EGR valve 13 in the second mode M2 ​​(S4).

[0036] If the answer to S3 is Yes, that is, for example, if the fuel injection amount is equal to or less than the second threshold value Th2, the ECU 20 selects the third mode M3 as the control mode and controls the EGR valve 13 in the third mode M3 (S5). Similarly, if the amount of deposits is greater than the third threshold value Th3, if the temperature of the EGR gas is equal to or less than the fourth threshold value Th4, or if the temperature of the exhaust manifold 7 is equal to or less than the fifth threshold value Th5, the ECU 20 selects the third mode M3 as the control mode and controls the EGR valve 13 in the third mode M3 (S5).

[0037] Then, the ECU 20 repeats the processing from S1 onwards based on the engine speed until the engine 1 stops (S6), and when the engine 1 stops, the series of processing (control) ends.

[0038] As described above, the ECU 20 as a control unit selects a predetermined control mode from the first mode M1, the second mode M2, and the third mode M3 according to at least the engine speed and the fuel injection amount, and controls the EGR valve 13 in the selected control mode.

[0039] In addition to the first mode M1 and the second mode M2, the ECU 20 also has a third mode M3 as a control mode for the EGR valve 13. Therefore, when the risk of deposits accumulating in the EGR valve 13 is low, for example, when the fuel injection amount is greater than the first threshold value Th1 and equal to or less than the second threshold value Th1 (No in S1, Yes in S3), the ECU 20 can select the third mode M3 to control the EGR valve 13. In the third mode M3, the EGR valve 13 is opened only during the on-period P1. Therefore, compared to, for example, controlling the EGR valve 13 in the first mode M1 (compared to fully closing the EGR valve 13), it is possible to reduce the amount of NOx contained in the exhaust gas discharged from the cylinder head 4. Therefore, when the risk of deposits accumulating in the EGR valve 13 is low, the ECU 20 can select the third mode M3 to control the EGR valve 13 to open it as much as possible, thereby reducing NOx emissions as much as possible.

[0040] If the fuel injection amount is equal to or less than the first threshold value Th1 (Yes in S1), it is considered that there is a high risk of deposits accumulating in the EGR valve 13. In this case, it is desirable to fully close the EGR valve 13 to suppress the accumulation of deposits in the EGR valve 13. From this perspective, it is desirable that the ECU 20 selects the first mode M1 as the control mode when the fuel injection amount is equal to or less than the first threshold value Th1 (S1, S2).

[0041] Furthermore, when the fuel injection amount is greater than the second threshold value Th2 (No in S3), it is desirable that the ECU 20 selects the second mode M2 ​​as the control mode from the viewpoint of reducing NOx emissions (S4).

[0042] On the other hand, if the fuel injection amount is greater than the first threshold value Th1 and equal to or less than the second threshold value Th2, it is considered that there is a low risk of deposits accumulating in the EGR valve 13. In this case, from the viewpoint of suppressing deposit accumulation in the EGR valve 13 while opening the EGR valve 13 as much as possible and reducing NOx emissions, it is desirable for the ECU 20 to select the third mode M3 as the control mode (S3, S5).

[0043] When the fuel injection amount is greater than the first threshold value Th1 and equal to or less than the second threshold value (S3), as described above, it is considered that the risk of deposits accumulating in the EGR valve 13 is low. However, if the actual amount of deposits is large, the accumulated deposits may prevent the opening degree of the EGR valve 13 from being appropriately adjusted to an opening degree that corresponds to the operating state of the engine 1. Therefore, when selecting the third mode M3 in S5 based on the determination in S3, it is desirable to take into account the actual amount of deposits accumulated in the EGR valve 13. In other words, it is desirable for the ECU 20 to select the third mode M3 as the control mode when the amount of deposits accumulated in the EGR valve 13 obtained based on the initial position of the EGR valve 13 is greater than the third threshold value Th3 (S3, S5).

[0044] On the other hand, if the amount of deposits is equal to or less than the third threshold value Th3 in S3, it is desirable for the ECU 20 to select the second mode M2 ​​as the control mode (S4) in order to reduce NOx emissions (giving priority to suppressing deposit accumulation on the EGR valve 13).

[0045] Furthermore, when the fuel injection amount is greater than the first threshold value Th1 and equal to or less than the second threshold value Th2 (S3), if the temperature of the EGR gas is low, there is a high risk of deposits accumulating on the EGR valve 13, and the accumulated deposits may prevent the opening of the EGR valve 13 from being appropriately adjusted to an opening that corresponds to the operating state of the engine 1. Therefore, when selecting the third mode M3 in S5 based on the determination in S3, it is desirable to take the temperature of the EGR gas into consideration in the determination in S3. That is, when the temperature of the EGR gas is equal to or less than the fourth threshold value Th4, the ECU 20 desirably selects the third mode M3 as the control mode (S3, S5).

[0046] On the other hand, in S3, if the temperature of the EGR gas is higher than the fourth threshold value Th4, it is considered that there is a low risk of deposits accumulating on the EGR valve 13. In this case, from the viewpoint of reducing NOx emissions (giving priority over suppressing deposit accumulation on the EGR valve 13), it is desirable that the ECU 20 select the second mode M2 ​​as the control mode (S4).

[0047] Furthermore, when the fuel injection amount is greater than the first threshold value Th1 and equal to or less than the second threshold value Th2 (S3), if the temperature (exhaust gas temperature) of the exhaust manifold 7 that discharges exhaust gas from the cylinder head 4 is low, the exhaust gas contains a large amount of unburned components, which increases the risk of deposits accumulating in the EGR valve 13, through which part of the exhaust gas passes as EGR gas. As a result, the accumulated deposits may make it impossible to appropriately adjust the opening of the EGR valve 13 to an opening appropriate for the operating state of the engine 1. Therefore, when selecting the third mode M3 in S5 based on the determination in S3, it is desirable to take the temperature of the exhaust manifold 7 into consideration in the determination in S3. That is, it is desirable for the ECU 20 to select the third mode M3 as the control mode when the temperature of the exhaust manifold 7 is equal to or less than the fifth threshold value Th5 (S3, S5).

[0048] On the other hand, in S3, if the temperature of the exhaust manifold 7 is higher than the fifth threshold value Th5, it is considered that there is a low risk of deposits accumulating on the EGR valve 13. In this case, from the viewpoint of achieving a reduction in NOx emissions (which takes priority over suppressing the accumulation of deposits on the EGR valve 13), it is desirable that the ECU 20 select the second mode M2 ​​as the control mode (S4).

[0049] [3. Duty ratio adjustment in 3rd mode] FIG. 6 schematically shows the relationship between the temperature of the EGR gas and the duty ratio (the ratio of the on-period to the off-period) when the EGR valve 13 is controlled in the third mode M3. Here, one cycle P (sec), which is the repetition unit of the on-period and the off-period, is made constant. Also, let the on-period when the temperature of the EGR gas is T1 (°C) be P11 (sec) and the off-period be P21 (sec). Let the on-period when the temperature of the EGR gas is T2 (°C) lower than T1 be P12 (sec) and the off-period be P22 (sec). Let the on-period when the temperature of the EGR gas is T3 (°C) lower than T2 be P13 (sec) and the off-period be P23 (sec).

[0050] In the third mode, from the viewpoint of reducing NOx emissions, it is desirable to secure the on-period and open the EGR valve 13 as much as possible. However, when the EGR valve 13 is opened, as the EGR gas temperature becomes lower, deposits are more likely to accumulate on the EGR valve 13 (the risk of deposition becomes higher). Therefore, in the present embodiment, when the temperature of the EGR gas changes as T1, T2 (<T1), T3 (<T2), the off-period in one cycle P is changed as P21, P22 (>P21), P23 (>P22). That is, considering the temperature of the EGR gas, from the viewpoint of suppressing the deposition of deposits on the EGR valve 13, in the third mode, it is desirable for the ECU 20 to increase the off-period in one cycle P as the EGR gas temperature becomes lower.

[0051] FIG. 7 schematically shows the relationship between the number of initialization steps, which indicates the initial position of the EGR valve 13, and the duty ratio when the EGR valve 13 is controlled in the third mode M3. As in FIG. 6, one cycle P (sec), which is a repetition unit of the on-period and the off-period, is constant. When the number of initialization steps is N1 (steps), the on-period is P14 (sec) and the off-period is P24 (sec). When the number of initialization steps is N2 (steps), which is greater than N1, the on-period is P15 (sec) and the off-period is P25 (sec). When the number of initialization steps is N3 (steps), which is greater than N2, the on-period is P16 (sec) and the off-period is P26 (sec). The amounts of deposits on the EGR valve 13 recognized by the ECU 20 when the number of initialization steps is N1, N2, and N3 are D1 (mm), D2 (mm), and D3 (mm), respectively. In addition, N1 <N2<N3であるため、D1<D2<D3である。

[0052] In the third mode, from the viewpoint of reducing NOx emissions, it is desirable to secure an on-period and open the EGR valve 13 as much as possible. However, opening the EGR valve 13 makes it easier for deposits to accumulate in the EGR valve 13. If the amount of deposits in the EGR valve 13 increases, the accumulated deposits may make it impossible to appropriately adjust the opening of the EGR valve 13 to an opening that corresponds to the operating state of the engine 1. For this reason, in this embodiment, when the number of initialization steps changes from N1 to N2 (> N1) to N3 (> N2), that is, when the amount of deposits changes from D1 to D2 (> D1) to D3 (> D2), the off-period in one cycle P is changed from P24 to P25 (> P24) to P26 (> P25). That is, from the viewpoint of appropriately adjusting the opening degree of the EGR valve 13 in consideration of the amount of deposits, it is desirable that the ECU 20, in the third mode, lengthen the off period in one cycle P as the amount of deposits increases.

[0053] [4. Adjusting the threshold] 8 shows a schematic diagram of a change in the first threshold value Th1 due to a transition of the control mode. After selecting the first mode M1 as the control mode, the ECU 20 preferably shifts the first threshold value Th1 in the direction of increasing the fuel injection amount. For example, if the first threshold value Th1 before the shift is Th1-a, the first threshold value after the shift becomes Th1-b. The amount of shift from Th1-a to Th1-b can be set as appropriate.

[0054] By adjusting the first threshold value Th1 in this manner, even if the fuel injection amount increases after the control mode has shifted from the third mode M3 to the first mode M1, the control mode is less likely to shift from the first mode M1 to the third mode M3 in a short period of time (because the first threshold value Th1 is substantially increased). In other words, the possibility of the control mode switching in a short period of time is reduced. This reduces the possibility that the control of the EGR valve 13 becomes complicated.

[0055] Furthermore, it is desirable that the ECU 20 shifts the first threshold value Th1 in a decreasing direction (of the fuel injection amount) after selecting the third mode M3 as the control mode. For example, if the first threshold value Th1 before the shift is Th1-b, the first threshold value after the shift becomes Th1-a.

[0056] By adjusting the first threshold value Th1 in this manner, even if the fuel injection amount decreases after the control mode has shifted from the first mode M1 to the third mode M3, the control mode is less likely to shift from the third mode M3 to the first mode M1 in a short period of time (because the first threshold value Th1 is substantially lowered). In other words, the possibility of the control mode switching in a short period of time is reduced. This reduces the possibility that the control of the EGR valve 13 becomes complicated.

[0057] 9 shows a schematic diagram of the change in the second threshold value Th2 due to the transition of the control mode. After the ECU 20 selects the third mode M3 as the control mode, it is desirable to shift the second threshold value Th2 in the direction of increasing the fuel injection amount. For example, if the second threshold value Th2 before the shift is Th2-a, the second threshold value after the shift becomes Th2-b. The amount of shift from Th2-a to Th2-b can be set as appropriate.

[0058] By adjusting the second threshold value Th2 in this manner, even if the fuel injection amount increases after the control mode has shifted from the second mode M2 ​​to the third mode M3, the control mode is less likely to shift from the third mode M3 to the second mode M2 ​​in a short period of time (because the second threshold value Th2 is effectively increased). In other words, the possibility of the control mode switching in a short period of time is reduced. This reduces the possibility that the control of the EGR valve 13 becomes complicated.

[0059] Furthermore, it is desirable that the ECU 20 shifts the second threshold value Th2 in a decreasing direction (of the fuel injection amount) after selecting the second mode M2 ​​as the control mode. For example, if the second threshold value Th2 before the shift is Th2-b, the second threshold value after the shift becomes Th2-a.

[0060] By adjusting the second threshold value Th2 in this manner, for example, even if the fuel injection amount changes to decrease after the control mode has shifted from the third mode M3 to the second mode M2, the control mode is less likely to shift from the second mode M2 ​​to the third mode M3 in a short period of time (because the second threshold value Th2 is substantially lowered). In other words, the possibility of the control mode switching in a short period of time is reduced. This reduces the possibility that the control of the EGR valve 13 becomes complicated.

[0061] [5. Supplementary Information] Although the above description has been given of an example in which there are three control modes for the EGR valve 13, namely, the first mode M1, the second mode M2, and the third mode M3, there may be four or more control modes. The ECU 20 may select one of the first mode M1, the second mode M2, or the third mode M3 from the four or more control modes in accordance with at least the engine speed and the fuel injection amount, and control the EGR valve 13 in the selected control mode. Therefore, for example, the multiple control modes for the EGR valve 13 may include a fourth mode in which the EGR valve 13 is fully open.

[0062] The third threshold value Th3 used in the determination of S3 in FIG. 5, that is, the third threshold value Th3 to be compared with the amount of deposits accumulated in the EGR valve 13, may be varied depending on the operating time of the engine 1. For example, the longer the operating time of the engine 1, the larger the third threshold value Th3 may be. It is expected that the amount of deposits accumulated in the EGR valve 13 will increase as the operating time of the engine 1 increases. For this reason, by increasing the third threshold value Th3, it is possible to make it more difficult to enter the second mode M2 ​​(normal control). In other words, it is possible to perform control that prioritizes the third mode M3, which has an off period in which the EGR valve 13 is fully closed, over the second mode M2.

[0063] 5, instead of comparing the amount of deposits in the EGR valve 13 with the third threshold value Th3, a condition for comparing the operating time of the engine 1 with another threshold value may be included. It is expected that the longer the operating time of the engine 1, the greater the amount of deposits in the EGR valve 13. Therefore, by comparing the operating time of the engine 1 with another threshold value, it is possible to obtain results equivalent to those obtained by comparing the amount of deposits in the EGR valve 13 with the third threshold value Th3, depending on how the threshold value is set.

[0064] [6. Notes] The engine described in this embodiment can be expressed as described in the following supplementary notes.

[0065] The engine of appendix (1) is provided with an EGR device that recirculates a part of the exhaust gas discharged from the cylinder head as EGR gas to an intake pipe that supplies gas to the cylinder head, The EGR device is an engine having an EGR valve that adjusts the amount of recirculation of the EGR gas, Further, a control unit that controls the EGR valve is provided. the control unit selects a predetermined control mode from at least a first mode, a second mode, and a third mode in accordance with at least an engine speed and a fuel injection amount, and controls the EGR valve in the selected control mode; the first mode is a control mode in which the EGR valve is fully closed, the second mode is a control mode for adjusting the opening degree of the EGR valve in accordance with the operating state of the engine, The third mode is a control mode in which an ON period in which the opening degree of the EGR valve is adjusted depending on the operating state of the engine and an OFF period in which the EGR valve is fully closed are repeated (at a predetermined ratio).

[0066] The engine of appendix (2) is the engine of appendix (1), When the two thresholds of the fuel injection amount that are set in advance according to the engine speed are a first threshold and a second threshold in ascending order, The control unit When the fuel injection amount is equal to or less than the first threshold value corresponding to the engine rotation speed, the first mode is selected as the control mode; When the fuel injection amount is greater than the second threshold value corresponding to the engine rotation speed, the second mode is selected as the control mode; When the fuel injection amount is greater than the first threshold value corresponding to the engine speed and is equal to or less than the second threshold value corresponding to the engine speed, the third mode is selected as the control mode.

[0067] The engine of supplementary note (3) is the engine of supplementary note (2), The control unit When the fuel injection amount is greater than the first threshold value corresponding to the engine rotation speed, When the fuel injection amount is equal to or less than the second threshold corresponding to the engine speed and the amount of deposits accumulated in the EGR valve obtained based on the initial position of the EGR valve is greater than a third threshold, the third mode is selected as the control mode, while when the amount of deposits is equal to or less than the third threshold, the second mode is selected as the control mode.

[0068] The engine of supplementary note (4) is the engine according to supplementary note (2) or (3), The control unit When the fuel injection amount is greater than the first threshold value corresponding to the engine rotation speed, When the fuel injection amount is equal to or less than the second threshold corresponding to the engine speed and the temperature of the EGR gas is equal to or less than a fourth threshold, the third mode is selected as the control mode, whereas when the temperature of the EGR gas is greater than the fourth threshold, the second mode is selected as the control mode.

[0069] The engine of supplementary note (5) is the engine according to any one of supplementary notes (2) to (4), The control unit When the fuel injection amount is greater than the first threshold value corresponding to the engine rotation speed, When the fuel injection amount is equal to or less than the second threshold corresponding to the engine speed and the temperature of the exhaust manifold that discharges the exhaust gas from the cylinder head is equal to or less than a fifth threshold, the third mode is selected as the control mode, whereas when the temperature of the exhaust manifold is greater than the fifth threshold, the second mode is selected as the control mode.

[0070] The engine of appendix (6) is the engine according to any one of appendices (2) to (5), After selecting the first mode, the control unit shifts the first threshold in an increasing direction.

[0071] The engine of appendix (7) is the engine according to any one of appendices (2) to (6), After selecting the third mode, the control unit shifts the first threshold in a decreasing direction.

[0072] The engine of supplementary note (8) is the engine according to any one of supplementary notes (2) to (7), After selecting the third mode, the control unit shifts the second threshold in an increasing direction.

[0073] The engine of supplementary note (9) is the engine according to any one of supplementary notes (2) to (8), After selecting the second mode, the control unit shifts the second threshold in a decreasing direction.

[0074] The engine of supplementary note (10) is the engine according to any one of supplementary notes (1) to (9), In the third mode, the control unit extends the off period in one cycle, which is a repeating unit of the on period and the off period, as the temperature of the EGR gas decreases.

[0075] The engine of appendix (11) is the engine according to any one of appendices (1) to (10), An engine as described in any one of claims 1 to 10, wherein in the third mode, the control unit extends the off period in one cycle, which is a repeating unit of the on period and the off period, as the amount of deposits accumulated in the EGR valve obtained based on the initial position of the EGR valve increases.

[0076] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these, and the invention can be expanded or modified without departing from the spirit of the invention. [Industrial Applicability]

[0077] The present invention can be used in work vehicles such as tractors. [Explanation of symbols]

[0078] 1 engine 2 intake pipe 4. Cylinder head 7. Exhaust manifold 10 EGR device 13 EGR valve 20 ECU (control unit) M1 First mode M2 Second mode M3 3rd Mode P period P1 ON period P2 off period Th1 First threshold Th2 Second threshold Th3 Third threshold Th4 Fourth threshold Th5 Fifth threshold

Claims

1. an EGR device that recirculates a portion of exhaust gas discharged from a cylinder head as EGR gas to an intake pipe that supplies gas to the cylinder head; The EGR device is an engine having an EGR valve that adjusts the amount of recirculation of the EGR gas, Further, a control unit for controlling the EGR valve is provided. the control unit selects a predetermined control mode from at least a first mode, a second mode, and a third mode in accordance with at least an engine speed and a fuel injection amount, and controls the EGR valve in the selected control mode; the first mode is a control mode in which the EGR valve is fully closed, the second mode is a control mode in which the opening degree of the EGR valve is adjusted in accordance with an operating state of the engine, The third mode is a control mode in which an ON period in which the opening degree of the EGR valve is adjusted in accordance with the operating state of the engine and an OFF period in which the EGR valve is fully closed are repeated.

2. When the two types of threshold values ​​of the fuel injection amount that are set in advance according to the engine rotation speed are a first threshold value and a second threshold value in order from the smaller one, The control unit When the fuel injection amount is equal to or less than the first threshold value corresponding to the engine rotation speed, the first mode is selected as the control mode; When the fuel injection amount is greater than the second threshold value corresponding to the engine rotation speed, the second mode is selected as the control mode; 2. The engine according to claim 1, wherein the third mode is selected as the control mode when the fuel injection amount is greater than the first threshold value corresponding to the engine speed and is equal to or less than the second threshold value corresponding to the engine speed.

3. The control unit When the fuel injection amount is greater than the first threshold value corresponding to the engine rotation speed, 3. The engine of claim 2, wherein the third mode is selected as the control mode when the fuel injection amount is equal to or less than the second threshold value corresponding to the engine speed and the amount of deposits on the EGR valve obtained based on the initial position of the EGR valve is greater than a third threshold value, while the second mode is selected as the control mode when the amount of deposits is equal to or less than the third threshold value.

4. The control unit When the fuel injection amount is greater than the first threshold value corresponding to the engine rotation speed, 3. The engine of claim 2, wherein the third mode is selected as the control mode when the fuel injection amount is equal to or less than the second threshold corresponding to the engine speed and the temperature of the EGR gas is equal to or less than a fourth threshold, and the second mode is selected as the control mode when the temperature of the EGR gas is greater than the fourth threshold.

5. The control unit When the fuel injection amount is greater than the first threshold value corresponding to the engine rotation speed, 3. The engine according to claim 2, wherein the third mode is selected as the control mode when the fuel injection amount is equal to or less than the second threshold value corresponding to the engine speed and when the temperature of an exhaust manifold that discharges the exhaust gas from the cylinder head is equal to or less than a fifth threshold value, and the second mode is selected as the control mode when the temperature of the exhaust manifold is higher than the fifth threshold value.

6. The engine according to claim 2 , wherein the control unit shifts the first threshold value in an increasing direction after selecting the first mode.

7. The engine according to claim 2 , wherein the control unit shifts the first threshold value in a decreasing direction after selecting the third mode.

8. The engine according to claim 2 , wherein the control unit shifts the second threshold value in an increasing direction after selecting the third mode.

9. The engine according to claim 2 , wherein the control unit shifts the second threshold value in a decreasing direction after selecting the second mode.

10. The engine according to claim 1 , wherein, in the third mode, the control unit extends the off period in one cycle, which is a repeating unit of the on period and the off period, as the temperature of the EGR gas decreases.

11. The engine according to claim 1, wherein in the third mode, the control unit extends the off period in one cycle, which is a repeating unit of the on period and the off period, as the amount of deposits accumulated in the EGR valve obtained based on the initial position of the EGR valve increases.

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